Sorry for the delayed reply--on the road until now.
Donn0128--I appreciate bluntness and am not pissed off by anyone with good intentions, as you seem to be. I am getting the sense that playing with the numbers to stay within weights is the difference between "in theory" and "in practice". It is starting to look as if a sub-30 footer by SpaceCraft with attention paid to weights and layout is the way to go.
APT--my truck specs were hand entered from the sheet my dealer gave me for my truck. I understand the various weights and want to be well within all of them--I do not want to cherry pick a few that work. I have the impression that airbags or other suspension upgrades may work well, but do not change the legal capacities of a truck once spec'd by the manufacturer.
Already own the truck--bought it knowing I would prefer to downsize planned rv than drive a stiffer or bigger truck. I understand others making a different decision, but this is mine. My wife, our German Shepherd, and I all together weigh 320 lbs--so, a little more allowance for the rv and a little less space needed for the three of us. We are not particularly thin, but we are short--I am the tallest at 5'4"--with a custom unit, we can save a lot of weight with lower ceilings (reducing the weight of the walls). Lower height would be limited only by re-sale considerations. I am thinking an even 6' in the bedroom and 6'4" in the living room.