I might suggest you not give up quite so soon. I'm an RV guy and work 80-10m with two different antennas. A G5RV that I throw up in the trees when I can, is the best and always works.
As you probably already know, RVs are RF noise factories. Between the lights to the inverter/charger/converter there's noise everywhere. Plus your RV neighbors are generating noise too so that's almost as much a problem as antenna issues.
We use a vertical 23' fiberglass multiband HF boat whip on top hinged to a mount for raising. The RV is like yours, fiberglass with metal framing so we added a 8X8 ground plane of copper window-screen glued to the top of the RV centered under the antenna and it is screwed to the frame at the corners. Antenna matches on everything we use with an ATR-30 tuner.
I can tell you that hitch mount and ladder mounts are not the best place and many have had experiences just like yours. SWR all over the place.
The guy that helped me a lot was Alan, KØBGhttp://www.k0bg.com
He put in contact with a couple of folks that were a great help and his website is a wealth of information on operating Mobile (which an RV is).