a 6.5 with mechanical pump would probably be the easy way to go. Considering the weight of your camper should do fine. If your going to tow/haul heavy Duramax for sure.
My first diesel was a 94 GMC K2500 6.5/5 speed. I bought a 36 ft fifth wheel and i pulled it but it was a chore. When I retired I picked up an 06 GMC D/A and it pulled that trailer a lot better. When we left out after living in the fifth wheel for 15 years it was loaded heavy. Scaled it at 24500 lbs. Donner Pass was first workout. Then across Utah, North Rim, and Santa Fe. Made it to East Tennessee where we are now.
Made a couple trips to Northern Virginia and now the fifth wheel is gone.
Lighter towing 6.5 but heavy go the Duramax
"The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government."
-Patrick Henry
A5150nut
2006 K3500 D/A
94 6.5 4x4 5spd Sold