Regarding the ability to store a fuel reserve onboard the vehicle; Before your readers consider an expensive custom military fuel tank (which may not meet DOT standards), they many want to consider an option that is already approved by the DOT and is very affordable.
As a race car and off-road truck enthusiast I’ve participated in many events where cars/trucks must meet Department of Transportation (DOT) certification before the vehicle can compete. A majority of the “modified” vehicles run gasoline and use aftermarket fuel tanks of various sizes. Depending on the style of racing many of the tanks have baffles to prevent “sloshing” and spilling, as well as mounting brackets to keep them secure in the event of a crash. The sizes of these tanks range from 2 quarts to 45 gallons, with everything in between. The fuel cells I’m referring to do not operate the same way a Home Depot fuel can does, and instead have a filler hole and at least one pre installed pickup tube where the liquid is pumped or drained into the engine. I could envision a system that drains via gravity or a pump into the primary fuel tank when needed.
A word of advice to anyone considering mounting an auxiliary tank in the interior of their car (including trunk), gasoline does have a fairly low vapor pressure, which causes it to turn to a gas (vapor) form easier then diesel or water for example. This effectively will cause a sealed tank to become pressurized in the heat, and an unsealed tank to emit lots of fumes. These fumes are what causes gas to be more flammable than some other petroleum products. In the old days, this problem was solved by simply venting the tank to the outside of the vehicle via a hose and a check valve. Regulations vary by year of vehicle, but generally do not allow for a tank to be vented into the atmosphere without either a carbon filter or through the combustion process. I’d recommend you visit your local reputable mechanic for specifics about your application. Hint: a local reputable race car builder is a good place to start asking questions. They are usually fountains of knowledge and are much easier to talk with than a factory dealer mechanic.
A good place to start looking for these tanks would be either SummitRacing.com, or Jegs.com. Both of these companies have excellent customer service and have been around for many years. Look for “fuel cells”. Prices range from ~$35 to ~$250. While you are at it, peruse their catalogs. These companies have many other automotive parts that could make your vehicle both more reliable and robust. By the way, I don’t work for either of them and don’t have any financial benefit.
Whatever you decide, do it correctly and stay safe. – Race Fan from Colorado