How get truck and TC with ample weight capacity

One other thought . . .

You're taking the right approach by trying to go minimal on the camper (non-slide, flexible on size) and robust on the truck (350/3500, maybe even drw), which provides best potential for favorable weight ratings.

This approach sure beats trying to put a giant camper, with multiple slides, on a half-ton truck. Hopefully nobody has tried such a thing!