A slideout unit is going to be too heavy if GVWR is your concern.
Look at northstar campers. The Liberty and Freedom are hardside TCs.
They will offer you what you are looking for with relatively low weight.
http://www.northstarcampers.com/online-catalog.php?headerbar=1&view=subs&parentId=15Look at the following link to get an idea of how the weight increases from DRY wt. to Wet wt. most of the weight gets carried by the rear axle. NOW ADD ALL YOUR STUFF to that wet weight avrg, = 500# more.
http://www.truckcampermagazine.com/truck-camper-buyers-guide/northstar-camperI would be more concerned about watching my rear axle being overloaded opposed to the GVWR.
You might need to upgrade the tires to a 10 ply E rated tire in a size that will offer you 3400-3700# each. ex: 265/75/16 E 3415#
compare weights of various sizes...
http://www.tirerack.com/tires/tires.jsp?tireMake=BFGoodrich&tireModel=All-Terrain+T%2FA+KO&partnum=675QR6ATAKO10&vehicleSearch=false&fromCompare1=yes&tab=SpecsOEM hub centric stock wheels should work, see if they have a stamp for their wheel weight rating. It might written in code where you will have to read it at a truck/tire shop.
If you are using aftermarket lug centric wheels with a hub spacer, then you need to look into that with truck professionals and make a decision. Your are carrying a lot of weight hauling a camper, its not the same as towing the weight.
Good luck, Bob