ive replaced it, althought to be honest i really cant remember if it was welded on or not, however i do remember osmesthing being welded on that was just a spot weld and all you had to do is take a drill bit and drill the holes, so either way its not a big deal(i think the nose panel is bolt on and the radiator support is a spot weld)
check your charcoal canister, thats what gets rid of the fumes from the gas tank and if its bad/saturated with gas it may do that