I've had many regular cab pickups, a few crew-cabs (four full size doors) and currently drive an extended cab (rear half-doors).
I won't go back to a regular cab. The longer wheelbase trucks tow a lot better, that's a simple physics thing, plus having somewhere besides the front seat to put stuff is really great.
By-the-book numbers say to buy a regular cab gasser, but I'd never go back to one of those for heavy camper plus trailer driving!
Get the diesel, extra cab. The numbers you need to pay attention to are the actual axle ratings and the tire load limits. You won't be exceeding those. And you'll have a truck that's far, far superior for the job!
Oh - if you plan on a crazy long extended trailer hitch to tow with that camper on, you really want a longer truck!! The shorter the wheelbase the worse it tows, the longer the hitch extension the worse it tows. Don't go buy the worst possible combo because the brochure appears to say it's best.
If you don't get a diesel, have fun crawling down the hills in low with hot brakes!
