Now, in addition to fuel prices over $4 a gallon, we have many rollbacks being built on current-model chassis like the Ford F550 and Chevy C5500 with inboard fuel tanks under the rollback bed.  Inboard fuel tanks (tanks between the frame rails) create an entire troubleshooting category of their own:  how to prevent fuel from splashing back in the filler hose when you fill the tank.

Eliminate kinks in the filler hose

The fuel filler hose needs to be more or less smooth, without kinks, so fuel can flow from the filler neck into the tank without splashing back.  Kinks often develop in corners.  Sometimes a kink can be eliminated or lessened by clamping and tying the filler hose in a different geometry.  Formed hoses, which come pre-bent, are less likely to develop a kink than straight hoses that have been adapted to the task.

Locate the filler neck at higher elevation than the tank

The fuel filler neck, which is the metal tube you stick the nozzle into when fueling, needs to be higher than the fuel tank in order for fuel to gravity-flow down the filler hose into the tank.  Rollback beds add to this challenge because the outboard edge of the rollback deck limits how high you can raise the filler neck.  Locate the filler neck as high as you can without hitting the underside of the rollback deck.

Avoid kinks in the vent hose

The vent hose is the small hose about the size of an automobile heater hose that runs alongside the larger filler hose.  The vent hose conducts air back up to the filler neck as you displace air out of the tank by filling the tank with fuel.  If the vent hose doesn't admit air, fuel will "burp" back up the filler hose when you try to fill the tank.  When vent hoses kink, it's often right at the point where the vent hose attaches to the fuel tank.  The best strategy is usually to use plastic ties to tie the vent hose to the side of the filler hose, and make bends gradual, rather than acute.

Of course, all the above strategies require the fuel filler neck to be mounted securely.  If the neck is hanging down below tank level, or tied to a makeshift steel rod that someone tack-welded to the chassis frame, it's not going to admit fuel at a satisfactory speed.  A properly installed fuel filler assembly will allow you to pump fuel at full speed without having to resort to such tiresome tricks as raising the rollback bed at the gas station.

Fuel filler hardware can be bought from Ford and GM.  In addition, Transfer Flow Inc. at (800) 442-0056 sells retrofit fillneck kits for Ford and GM commercial cab and chassis.