Jon,
Wyn and I got waylayed in Evanston, WY by a winter storm, we were lucky as we found the only RV park still open prior to winter shutdown. A Canadian bus conversion couple came in next to us, besides the storm, they had a problem with their very earlier version of an aqua-hot system. I troubleshooted it for them and found their temp controller was NG, since they could not find a 24VDC version they had to run their engine to keep warm, that was a Friday night. Saturday morning we found 22 pints of transmission fluid had leaked from a hose that had rub against the measuring tube. We were able to find the only two hoses in town and replaced them and the fluid, so at least they had heat. You got to watch them hoses.
Safe Travels,