Gas tank and exhaust routing

[DarkFlounder]

Sometime this year, I'm gonna replace the bed (eventually, the rust will stop holding it together), and while I've got the bed off, I'll probably put in a new under-bed gas tank.

I really like the 41gal Suburban tank between the frame rails I saw another post about. Without having climbed under and measured the space, would a tank this size be better placed forward or behind the axle?

And since I'm eventually going to have the exhaust redone (about as many holes and rust as the bed), I'm thinking about having the exhaust routed outside the frame rails (so they'll not be directly under the tank) and dumping out in front of the wheels.

Any thoughts? Should I stop thinking about the truck and get back to work (it's Friday after 4pm, leave me alone).