Well, it's been a while since I posted on this, but here's an update.
When light (mostly empty, maybe 1000 lbs in it) The rig tows well, handles nicely, and is just fine. We of course loaded it up to about 4000 lbs, and had it well stacked to the ceiling. This was not as good. There was significant slow speed tilting over semi-rough terrain. Enough to make one worry. It definitely became unruly offroad with side to side sway. I wouldn't be doing that again if I was me.
I'm sure it was all a very high CG problem. If I had to do it all over again, I'd consider the dual axles if I wanted to go off road, and I'd consider pulling it with a 5 ton versus a deuce. Although it's well within the deuces weight capacity, it does make for some slow going up hill.
Everything else about it works awesome. It's still water tight, still electrically sound, and still lots of fun to use for camping in. All we have is an air mattress on a shelf that runs side to side in the front of the trailer, and the underside of it doubles up for storage. Great rig!