2016 ram 3500 dully??? gaser or diesel???

We are looking into a truck a camper and the diesels cost you payload, My current Chevy diesel pulls my current fifth wheel great but can not handle the 5k truck camper we are looking at. We want to keep the fifth wheel for a few more years but will only be towing it a few hundred miles a year and do our traveling with the truck camper. The only truck configuration that can handle both comfortably is a ram Crew cab DRW 6.4 hemi 4x2 14000lb gvwr it has the payload for the truck camper and rated for the fifth wheel towing, I think it is near 16 K for towing. I know it wont pull like my duramax but I have to give up either weight capacity or pulling power. The diesel and 4x4 really cuts into what you can carry. I am not worried about resale if I do this right it will our truck for a long while I would not spend this much money on a truck with either the 6.4 or diesel and not plan to keep the thing ten years or more . I love my diesel and tows great but I used to tow this same trailer with the 8.1 GM big block which the 6.4 and the 8.1 are close the 8.1 having a bit better numbers. right now I am leaning to the 6.4 but reading more towing stories