Tonneau covers are really popular on many pickup brands. However, the challenge is that every truck brand and every aftermarket tonneau cover provides a slightly different fit height when covered. That means no single tonneau cover offers a universal height above your pickup bed.
This challenge can make it really difficult to find a good transfer tank, auxiliary tank, or toolbox combo that fits cleanly underneath your tonneau cover. This article will provide some general guidance about height ranges for tonneau covers. It will then provide a list of some of the best under tonneau cover fuel tank options.
General Tonneau Cover Height Ranges
Your truck brand and whether your tonneau cover is an original manufacturer cover or an aftermarket cover makes a big difference in the available height underneath your cover.
In general, you will find that most tonneau covers will have the following height range underneath the cover when its closed over your bed:
- 17 inches of height to 21 inches of height.
Because of the wide range of heights, it’s really important to measure the actual height underneath your tonneau cover before you make a decision on a fuel tank.
Additional Tonneau Height Considerations
Auxiliary fuel tanks and transfer tanks all have slightly different designs that can impact the available height you have underneath your tonneau cover. As you are considering options make sure to consider the following factors:
Some tanks have a filler neck on the top of the tank. This can add an extra 1 to 2.5 inches to the overall height of the fuel tank.
A good option to look for is a filler neck that is either inside the top cover of the fuel tank or designed on the outside of the fuel tank.
Take a close look at your tonneau cover. Softer covers will have some flexibility and give which will allow you to increase the overall height of your fuel tank underneath the tonneau cover.
If you want a tank to hold gas, ethanol, methanol, kerosene or aviation fuel, you will need to choose an option that is DOT approved to hold a non-diesel fuel.
Best Under Tonneau Cover Fuel Tanks
The following fuel tanks all have limited height designs that make them well suited for use underneath a tonneau cover. Each tank has a range of heights, but make sure to measure the height of your closed tonneau cover.
Under Tonneau Transfer Tank with Fuel Pump
Transfer Flow offers a really convenient option for both a transfer tank and fuel pump that both fit underneath a closed tonneau cover. This transfer tank is DOT approved to carry your choice of gas, diesel, or kerosene.
Most transfer tanks include a top mounted fuel pump. The challenge with this design is that the fuel pump can add an extra 9 to 10 inches of height when mounted on top of a transfer tank. This creates a situation where the transfer tank may fit underneath a tonneau cover, but the top mounted fuel pump cannot fit under a tonneau cover when mounted on the tank.
Transfer Flow solves this problem with a side mounted fuel pump. The side mounted fuel pump allows the transfer tank and the fuel pump to comfortably fit under most standard tonneau covers.
The transfer tank does include a 2.5 inch fill neck on the top of the tank, but this fill neck is included in the listed height of the tank. Transfer Flow offers 4 size options for this tank, but only the 40 gallon size will fit under a tonneau cover with a total height of just 17.5 inches.
The 40 gallon Transfer Flow transfer tank includes the following:
- 40 gallon DOT approved steel transfer tank with side holster for fuel pump.
- 12V GPI 8 GPM transfer pump with 12 foot hose.
- Black powder coat finish.
When comparing the Transfer Flow tank with other tank options, you need to add in the price of a fuel pump and black powder coat to the price of the tank since most other tank options list the price of their tank without the cost of a fuel pump or a black powder coat finish.
Click the link below for more details on the 40 gallon Transfer Flow under tonneau cover transfer tank:
- See Tank: 40 gallon: 40 inches long x 23 inches wide x 17.5 inches high
You can also compare all Transfer Flow 40 Gallon Fuel Tanks.
Fuel Transfer Tank Under Tonneau Cover
ATI’s DOT Approved transfer tank is available in sizes that range from 38 gallons to 110 gallons. Some smaller sizes offer low height options that start at 12 inches to 19 inches.
Keep in mind these fuel transfer tanks include an outside fill neck, so you need to add 2.5 inches of height to the tank to account for the fill neck.
Note: ATI transfer tanks have a top mounted fuel pump. If you want the fuel pump to fit underneath a tonneau cover you need to select the "ATI Tank Notch for Tonneau Cover" on the product page.
The ATI tank notch is a custom modification that removes a cube shaped chunk of the transfer tank at the fuel bung. This reduces the height of the fuel pump when attached to the tank.
Note: ATI rectangular fuel tanks that are 50 gallons or less ship by UPS.
We will highlight a few of the tank sizes with the lowest heights:
- TTR38: 38 gallon – 48.5 inches long by 11 inches wide by 19 inches high
- TTR42: 42 gallon – 48.5 inches long by 19 inches wide by 12 inches high
- TTR43: 43 gallon – 58 inches long by 12 inches wide by 16.5 inches high
- TTR46: 46 gallon – 57 inches long by 12 inches wide by 16.5 inches high
- TTR50: 50 gallon – 36.25 inches long by 19 inches wide by 19 inches high
- TTR58: 58 gallon – 58 inches long by 21 inches wide by 13 inches high
- TTR62: 62 gallon – 60 inches long by 21 inches wide by 13 inches high
- TTR77: 77 gallon – 57 inches long by 18 inches wide by 19 inches high
Compare all ATI Fuel Tanks by dimensions with our size guide.
DOT Approved Under Tonneau Cover Transfer Tank
This transfer tank includes a built in lower height compartment for the transfer pump (sold separately).
This unique design includes a lower height area for the transfer pump to help keep the overall height of the tank to a minimum. This design lets you close your tonneau cover while keeping your fuel pump attached.
We recommend using the 12V 15GPM Fill Rite pump with this tank. The Fill Rite pump adds 10 additional inches of height to the fuel pump when attached to the top of the tank.
The full specs of both tank sizes are highlighted below:
AT41RBR-TF: 41 gallon – 60 inches long by 18 inches wide by 14 inches high (designed for use with roll-top bedcovers (canister style / soft covers).
- AT38RBT-TF: 38 gallon - 60 inches long by 12 inches wide by 15 inches high (designed for use with standard tonneau covers (hard covers).
*Both tanks have a notch on the lower length corner of the tank which reduces the lower level length to 54 inches. The top level length is 60 inches.
Check ATTA Transfer Tank dimensions.
Low Height Auxiliary Tank
Possibly the smallest height option available is this auxiliary fuel tank offered by ATTA. This tank is designed to fit directly below an existing truck toolbox. With a height of just 9 inches, this is a great option to keep a small fuel tank below your tonneau cover.
- AT30TB-SB: 30 gallon – 60 inches long by 21 inches wide by 9 inches high
- AT38TB: 38 gallon – 60 inches long by 21 inches wide by 9 inches high
See all Under Toolbox Fuel Tank options.
Aluminum Transfer Tank Under Tonneau Cover
ATTA offers a wide range of sizes that start at 20 gallons and increase all the way to 87 gallons. This is a great option if you want to keep gas, methanol, ethanol, kerosene or aviation fuel.
Not all of the sizes fit underneath a tonneau cover. The primary sizes that would work with a tonneau cover include:
- AT45RTF: 45 gallon – 60 inches long by 12 inches wide by 15 inches high
- AT60RTF: 60 gallon – 50 inches long by 20 inches wide by 15 inches high
- AT80RTF: 80 gallon – 60 inches long by 18 inches wide by 18 inches high
- AT87RTF: 87 gallon – 60 inches long by 18 inches wide by 19.5 inches high
Under Tonneau Cover Tank Toolbox Combo
This Fuelbox tank provides plenty of room under a tonneau cover with a height of just 17.5 inches. You have the option of adding a fuel tank capacity of 40 gallons, 45 gallons, or 55 gallons with this option.
The smallest option has just 20 inches of width and the largest option increases the width to 20 inches. The full measurements for each size are highlighted below:
- FTC44T: 40 gallon – 62 inches long by 20 inches wide by 17.5 inches high
- FTC60T: 45 gallon – 62 inches long by 23 inches wide by 17.5 inches high
- FTC70T: 55 gallon – 62 inches long by 20 inches wide by 17.5 inches high
Compare all Fuelbox Tank Toolbox Combos by size.
Diesel Auxiliary Fuel Tank Under Tonneau Cover
If you need extra fuel capacity and have a tonneau cover that offers higher than average space, the L-Shaped auxiliary fuel tank by Fuelbox is a great option to consider. This fuel tank is typically used to fit underneath an existing truck toolbox.
Keep in mind this tank has an outside fill neck on the top of the tank which adds an extra 2 inches of height to the fill cap. The full measurements of the two sizes are highlighted below:
- LT60T: 55 gallon – 53 inches long by 23.625 inches wide by 19 inches high
- LT70T: 70 gallon – 53 inches long by 28 inches wide by 19 inches high
Diesel Auxiliary Fuel Tank Under Tonneau
This tank offers a tapered design that minimizes the bottom length of the tank. The capacity sizes range from 40 gallons to 85 gallons. However, the 50 gallon size offers a very low height of just 15 inches which is ideal for being fit underneath a tonneau cover.
The other sizes also offer a modest height of just 19 inches of height, but you need to double check that you can fit these options. The full measurements for each option are highlighted below:
FT50: 50 gallon – 60 inches long by 16 inches wide by 15 inches high
- FT47: 40 gallon – 62 inches long by 10 inches wide by 19.5 inches high
- FT70: 68 gallon – 60 inches long by 19 inches wide by 19.5 inches high
- FT90: 85 gallon – 60 inches long by 25 inches wide by 19.5 inches high
Roll Top Auxiliary Fuel Tank
ATTA offers a similar minimal height fuel tank for those people who prefer an auxiliary tank. This tank is offered in two sizes which offer great fuel capacity at a minimal height of just 14 inches.
- AT45L-RT: 45 gallon – 60 inches long by 18 inches wide by 14 inches high
- AT72L-RT: 72 gallon – 60 inches long by 25 inches wide by 14 inches high
You can also visit our full selection of Fuel Transfer Tanks.