My 20' enclosed has a 10k lb GTWR and weighs about 3500 lbs empty. My trailer typically is loaded 6-8K lbs and I would not think of using something other than SuperHitch and double truss extension (SuperTruss). This is my second go around with this Torklift gear and it has not disappointed me.
BTW: Most 3500 DRW rear axles will be close to their limit while hauling a Host Mammoth. You will have have to watch what you load in the camper and how you load the trailer to avoid overloading an AAM 11.8 or Dana 80.
If you go with a pickup, you will need a 42" extension to clear the Mammoth overhang, but may not be able to fully open the cargo tray with a trailer in tow unless you go to a 48" length. If you get a chassis cab, you will be able to slide the Mammoth almost 9' on a deck before you have interference, so your extension can be shorter.