Over 8000 lbs dry and 36' long, Your way out of the half ton range IMO. I agree with you that the brochures say some of the half tons can tow that weight but you couldn't make me do it with my family on board.
Your going to be in the neighborhood of 9000-9500 loaded, more if you fill water tanks. The 36" and that weight would make me to consider a dually. Your likely ok with a HD 3/4 ton. A diesel would be a good choice if your pulling any hills or just want a little better mileage and power.
Nothing worse than the tail wagging the dog and I'm one of the overkill on the truck school of thought guys to eliminate problems.