Hmmm... There is a bit of a wide gap here to fill in. What kind of camper? (Travel trailer, 5th wheel, Pop-up?) Then your truck purchase will be based on the GVWR of the RV you decide to buy.
The first thing I would do is go directly to several dealers and walk through several RV's. Play house for while in each one. Flop on the bed see if you fit. Think about cooking a meal is there enough counter space? How about the bathroom can you get in and out of the bathroom, shower/tub ok? Because this is going to be your home and you better be comfortable with it.
As for the truck its always best to to have to much tow vehicle than not enough. I would suggest that 25' foot and up you consider a diesel truck for tow vehicle. It best to have a nice and heavy tow vehicle then you can control your RV better. It about enjoying your travels not having a white knuckle ride because the tow vehicle is too small for the beast behind you. If you got a large RV like my own which is a 31' foot I would suggest exhaust brake for the Western mountain states sure saves the brakes a bunch!
