[Accelo]

If it wasn't for having to have a method to fill the darn tank moving the tank to the rear would be a no brainier. I painted my truck and thought "I will deal with it later." That was the biggest mistake I made in building my truck.
The cheap China tanks give no credence to filler location. Right in the middle of the floor, a foot froward from the tail gate, was jut fine according to them. The tank I purchased even installed the attachment brackets welded on square to the tank, even thought its mounted on a tapered section of the frame. So the tank hit the bottom of the bed cross-member.
Relocating the tank is a major engineering headache. Don't think you can just throw it in the back and it's going to look and function great. If you don't have the time and money, to do it right, I would keep the tank in the stock location and spend my funds elsewhere.