Paul,
When you stated your concern about ELC compatibility with the Aqua Hot, I am assuming that you are only referring to the engine coolant heat exchanger in the Aqua Hot. If so, the is no compatibility issues with using ELC coolant in your coach. However, if you were considering using ELC in the Aqua Hot unit itself, Steve is right, that is unsafe. The Aqua Hot in your coach does not have a double wall heat exchanger for the domestic water supply like the earlier units, so you can only safely use non-toxic boiler fluid.
Gerald