One way to avoid that hassle is to simply build you an 3"x4" angle iron frame that is the dimensions of the bed. Use a 5-lug #3,500 axle and standard trailer springs, a 2" coupler, a standard 4-pin flat wiring connector, and a $25.00 tongue jack. Bolt your bed to the frame at the standard bed mounting points (weld the mounting ears to the trailer frame and bolt the bed to those). You'll have a very stout frame that will allow an even higher load carrying capacity than if you went and bent the truck frame and used the pickup rear (lots of unnecessary weight there!!!). Use the same bolt pattern as the truck and you'll only have to carry the one spare wheel/tire.
Makes for a much nicer looking and towing unit! You might consider electric or surge trailer brakes, either way. Depending on your state law, you may require them. If your state requires a title, getting a title/tag on what would be considered a home-built trailer is no big deal, and the state would assign a VIN# to it, in that case.
Good luck, whichever way you go!
