My swb has the fuel tank under the drivers seat and it stank of petrol, especially when it had just had some more fuel put in it. Had a look under the drivers seat and found that some previous owner had replaced the tank breather hose with a piece of green garden hose. Instead of attaching this to the fuel filler pipe, it terminated inside the truck cab behind the seat backs so all the fumes from the tank were where you had to sit. I guess the previous owner wasn't a smoker.