[mr48chev]

I don't think the heat is as much of an issue as the inconvenience if you have to drop the tank, Never heard of a 58/60 something Impala or a Mustang catching fire because the muffler dude ran the pipes under the gas tank.

You almost have to arm wrestle the muffler shop guys here to have the tail piped end up straight out under the bumper on a truck rather than off to the side behind the rear tire. As many late models around here run canopies on the bed and people might ride in them they want the exhust out in the slip stream rather than straight out the back where it might roll right back into the bed of the truck.