My Host Mammoth is 4712 lbs dry. By the time you add 60 gallons of water, occupants and personal gear, you're pushing 6000 lbs. The 3500 will be able to carry it, but don't plan on towing anything with tongue weight at the same time using that truck.
The 6.4 Hemi will do fine just carrying around the high profile camper even if it does sing pulling grades. If you plan to tow behind this combination, you need to look at the 6.7 CTD. Although the gasser is lighter than the diesel, all the weight is up front. In real world use, that rear axle will be loaded about the same regardless of your engine choice.