Might as well toss in my $.02. If you're going to retain your stock 53 rigid seat I'm hard pressed to see what you're going to have room to store. If you're getting fumes it's time to replace the tank anyways!
IMO the cab is the best protected location for a tank. Hanging it out in the rear with exposure on 5 surfaces just doesn't register as an upgrade. I guess it's just another one of those calls, where each individual makes his own decision. The price of a new stock tank (if your's is leaking) in the long run, will be money well spent.
