What 5th wheels have strong frames for double towing?

Paul, I used a commercially manufactured receiver rated at 20000 trailer weight, and 2000 tongue weight. That part is bolted to a 1/2" thick steel plate which is part of the hitch assembly I built. I don't know what the rating would be for my hitch, but I know that a 5000 pound trailer doesn't stress it or the trailer it's attached to.