Been running a 2005 8.1L 3500 SRW with a ~4000lb wet Eagle Cap 950 since late 2006. I added Rancho adjustable shocks but not sure I noticed a huge improvement. I'm sure they are better than what OEM shocks would be once worn out. No issue with power even with a 2k trailer in tow. I've only checked the mileage a couple times and it's solidly in the 8's with mixed freeway and back roads.
Only ~70k miles on the truck with a MAF sensor, oil pressure sender and coolant cap replacement so far.
If you are looking for "any camper you find" you will need a dually or limit your choices to ~9.5' campers or less.