Gerald,
many thanks for a very concise summary of all my diatribes. One question I havent been able to answer is where does the heat for the basement heating duct come from? Is it from the radiator fan mounted in the coach furniture behind the co pilot seat? If so we can keep the basement warm when operating the Hurricane 's water pump (Coach heat) and heating the water with the Seaward electric water heater.
You have answered my question re "Preheat" on my Marquis switching on a circulating pump in the engine space. Thanks again, Happy New Year , jeremy