I am a gmc duramax owner .
for your unique usage it seems to me that a ram mega cab with the cummins diesel is the first place to look .
one of my buddies has one and they have lots of room .
used rams are less money than the same vintage duramax .
cummins diesel will be much quieter inside while towing than any gasser .
resale is better on high mileage diesels than high mileage gassers .
I think you will lose less for depreciation when you factor in 25,000 additional miles .
the advantage of having the pickup bed for camp gear like bbq, propane tank , ez-up , beverage cooler , will pay off while your are mobile.
a 9200# gvw tow vehicle pulling a 7600# gvw tt is better than a 7600# gvw tow vehicle pulling a 9200# gvw tt. physics 101 ...