need rough guideline for what size TV for a fifth wheel

Well, since terms like "dry" are pretty much useless, and regardless of how you think you pack, pick a truck to handle the GVWR. You may or may not actually hit the GVWR, but guaranteed you will not come close to those mystical dry numbers. Fifth wheels generally varry 20-25% of their total weight as pin weight. Meaning directly over the rear axle. Add hitch weight and you can be over weight limits of most any 2500 truck.