Yeah tires are spendy, but the short box in my mega seems to be fine. It's an 8' 6 camper, and all of it's weight is up front. I just have the camper chained to the frame. I'm not sure what the gvwr is, or what my tires are rated at. I've been up & over many passes with it over the last few weeks, and it seems to be fine.
The camper weighs just under 3,000 lbs dry, and I keep the airbags at about 70psi to keep my fender flares from rubbing on the tires.

 

thats a beautiful *** truck. congrats! wish mine was a diesel [>:]