Newmars (Mountain Aire, etc) are very well built, high end units. They're also extremely heavy for a given length. If the advertised dry weight of the unit you're considering is 10,000 lbs, you'll be lucky if it weighs less than 12,000 lbs when you hitch up. At 20% pin weight, that will put 2,400 lbs on the truck as GVW. Since you only have 8,800 lbs GVWR to work with, the loaded truck with hitch, fuel, passengers, baggage, etc. couldn't weigh over 6,400 lbs if you're going to stay under your GVWR. If you have a 16,000 lb GCWR, I'm afraid you'll never have a chance to stay under it.
Maybe this matters to you, maybe not. I'm just presenting the numbers so that you can make an informed decision. Our 5ver has a 10,900 lb "dry weight" but is close to 13,500 lbs on the road with dry fresh and waste water tanks. We're running 10,380 lbs GVW (10,500 lbs GVWR) and 21,180 lbs GCW (21,500 GCWR).
Rusty