Unless you are spilling a lot of fuel when you are filling up there shouldnt be raw fuel all over. You will get some oil residue from the exhaust pipe but that will be concentrated on the pipe side of the truck. If you have a lot of wet fuel on the chassis I would check all the fuel lines to make sure they are on all the way and there are no holes. Also check the tank to make sure there are no cracks and that the lid is closing tightly so the fuel isnt spilling out the top while its bouncing around