op wrote:
I understand DRW is the preferred way to do this, but how much camper could I expect to haul well,without wishing I had bought smaller...?
Your 3500 srw GM has a 7050 rawr which includes wheels/tires and rear spring pack. Of course we know the tires capacity but I'm not up on GM wheel or rear spring pack ratings on gm trucks. Exceeding a wheel/tire or rear spring rating full time ain't real smart.
You have the truck so drop by a set of scales and weigh the trucks front and rear axles separately. That way you will know the trucks actual rear axle payload as it may carry all the TC weight.
example; ...Many late model 3500 srw gm owners report a 3200-3400 rear axle weight which leaves approx 3600-3800 lbs for a payload.