I doubt there are any stability problems with that type of hitch/trailer, after all UPS logs millions of miles a year pulling triples like that. I do wonder about clearance on sharp turns (like in a parking lot, not on the highway), depending on how much overhang you have back to the hitch on the truck. Maybe no different than a short tag trailer with a lot of overhang, you have to be careful there too. Would definitely be a ton cheaper than a stacker type trailer and would have room for all the toys you want. Offroad stuff would drive right up, and you can also put a liftgate on the back if needed.
In my opinion it would come down to how you use it, and where you have to maneuver it into. You are very limited as to how far you can back straight up, and zero chance of backing it into a parking slot at the truckstop or a campspot or your driveway. You will have some very limited maneuverability backing up, but for the most part it will be drop it where it is easy to pull up, and rehook when you are ready to go. Also keep in mind you generally can't just unhook the pintle and pull away, you will need to pull the dolly out from under the trailer before unhooking. Just ask an old trucker that tried it and got launched like a slingshot. Read up on the doubles/triples section of the cdl manual:
http://www.publicsafety.ohio.gov/links/HSY7605.pdf
Yeah, I know it's an RV and you don't need a cdl, but the mechanics would be like hooking up the rear trailer in a double setup.
Not a bad idea.