Do you have to have a pickup for a 5th wheel? Do you want/need 4wd? How heavy of a trailer?
I know tons of people on this site say they pack all the seats in a crew cab and it works great. I wouldn't want to do long trips like that personally. Sounds like you are not ready to do that either.
2500 Suburban or Ford Excursion. If you are willing to spend some money and travel for a super clean older truck, you can find some low mileage models.
1 ton van. If you need 4wd, there are companies that do conversions.
https://duramaxsuv.com
Considering the current diesel market, they have decent prices on duramax converted gmt800 and gmt900 suburbans. Basically a frame off rebuild that you can customize as you want and your wallet can handle. Really nice factory style installs where everything works like it would in a duramax pickup.
If you want new, and you need a 3/4-1 ton crew cab, a Dodge mega cab is going to be the most room you can get.