Tow capacity won't be your issue with the 2500 diesel, your payload will be. Ballpark you will be maxed out at about a 10,000lb TT. That will get you about 1200-1300lbs tongue weight then add your passengers, anything in the bed, tonneau cover, etc. If you pack light and only have 2 of you in the truck you could probably get closer to 12,000lbs. I towed my step-sons brand new 2021 Grand Design Imagine 3250BH. Dry weight was about 8500lbs. We weighed it on the CAT scales and it was 9300lbs. We had 1100lbs tongue weight and the truck was at 9100lbs. There were 3 of us in the truck (about 700lbs total) and a full tank of fuel. I have the 6.4 so add about 800lbs for the Cummins and I would have been right at about 9900lbs so right at max GVWR for the 2500. I have 2973lbs of payload according to my door sticker so my truck has a 'dry' weight of about 7100lbs so we had an extra 800 or so with passengers, tools, etc.
You should be good with the TT's you mentioned but if you plan to go bigger or plan to go with a 5th wheel I would definitely go with the 3500. 2500 Cummins will be pretty much maxed out with just about any 5tth wheel. Adding airbags will help it feel better but won't raise your capacities
Hope this helps.
Truck empty. The other 2 guys were at the dealer but weighed 420lbs combined so add that to these weights:
Truck with WDH and bars connected:
