A 3500 srw Ram has a 7000 rawr that will be carrying (any truck) most if not all of the truck campers weight. Front axle isn't that big of a player with heavy camper hanging out back.
A 3500 srw crew cab rear axle can weigh around 3500 lbs which leaves 3500 lbs for a loaded truck camper.
Those 4000-4500 lb payloads on 350/3500 srw trucks are a gvwr based payload (front and rear axles) will overload any of the one ton srw trucks rear axle.
Rear air suspension is a good option if available.
The Ram Mega cab comes only with a 6' 4" bed.
Its been my experience anything over 140" wheel base rides/handles just as well, if not better, than a 170' wb when all the load is on the trucks rear axle.
I would suggest a one ton drw with those big 9700-10500 lb rawr for carrying a 3800-5000 ln truck camper.