With the truck you have, your gross combined rating should be around 23~24K and will not be your limiting factor. What will be your limiting factor is going to be your rear axle weight rating(or tires actually). The setup in my signature has a rear axle weight without a trailer of around 7800#~7900# which was fine with LT285/75R17 DuraGrapplers but once I hooked up my trailer and the associated hardware it's ~9000# (or more depending how I set everything up) thus the 19.5s. So, if you want a slide you will probably want to go to 19.5s.
As many have said already, many short bed truck campers are going to have a significant overhang and will require a weight distributing hitch to minimize the amount of additional weight getting transferred to the rear axle. A quick and dirty way to determine how much weight a conventional hitch will add to the rear axle (in addition to the ball/hitch weight itself) is to multiply the hitch/ball weight by the distance from the ball to the rear axle divided by the wheelbase of the truck. With a weight distributing hitch you can dial this additional weight above the base ball/hitch weight away.
Or just go to this persons web-site and enter in the numbers...they also have a nifty module for estimating axle weights for the truck camper only scenario...
http://www.visualsc.com/hitch_calc.htm http://www.visualsc.com/tc_calc.htm I think it's put together by one of our fellow member's...haven't had the time to connect the dots though.