Any 2500/250 or 3500/350 will work basically the same and just fine.
If you're looking used, you'll have far more 3/4 tons to choose from.
And for your purposes, the only difference will be the capacity of the stock springs between the 2 classes of truck.
And yes ALOT of people upgrade the rear suspension of their trucks. It's normal and acceptable regardless of what the rvnet weight cops will tell you! lol
That said, given the option if buying new, a 3500 doesn't really cost more and would be slightly preferable.
One truck I wouldn't really consider is a Ram 2500 2014 or newer, due to the rear coil spring suspension. It too can be upgraded and will likely be fine with a lighter camper like yours, but it's not ideal and purportedly won't handle body roll (the main negative characteristic of hauling a truck camper) as well, by design.
