Im going to be as blunt as I can, but I will probably still piss you off. But here goes!
Your going full time, meaning your going to have everything you own in the trailer. That tells anybody with common sense that any RV you have is going to be running at or very near max. Its just the nature of people. Clothes, food, chairs, grill will add up way faster than you can imagine. Yea, you might end up under the trailers GVWR, but based on all the stuff I see other full timers carrying I doubt very much it will happen. Brochure pin weight is listed at the trailers dry weight. Figure it out for yourself. 20% of 10,800 is about 2160 pounds. So even the brochure is probably light. Having owned a Fox I can tell you for certain they are heavy to start with, and your going to not be happy. While you might be able to take each and every little item you load into a fiver and weigh it, then total all item weights. Why? It is far easier to error on the side of caution and take the trailers GVWR, using 20% of that as pin weight. Generally accepted fifth wheel pin weight is between 18 and 25%. So 20% is a reasonable number.
We are not full timers, but do spend a good number of days a year out.
My current fiver has a GVWR of 13,750 pounds and scales at 13,500 pounds. BTW brochure pin weight is 1750. Actual pin weight is north of 3000 pounds. Get the idea? If your insistsnt on a 2500 series truck your going to be limited to fivers with a GVWR around 10,000 pounds. Maybe pushing that a bit, but doing so your just asking for trouble.
My original truck was also a 2500HD. It took me three years before I upgraded to a dually and I have never regretted for one minute that decision. The towing the same trailer with two differe trucks was night and day different.