How can I calculate what size 5th wheel I can tow?

You will not have enough payload. If you add 1,500 pounds to the dry weight. This is easy to do. You will have a 2,902# pin weight at 20%. This does not include the hitch or any passengers or stuff. I would prefer to be able to use all ccc my 5er can give without overloading the TV. This 5er fully loaded at 16,000 pounds is in dually territory for me.