Hi Phil,
I solved the heat distribution with twin window fans replacing the cold air return grill. Cost was minimal. I find the propane furnace fan on the noisy side.
The cheap heat system is either/or and as sold OEM can not use the propane furnace as a back up, should shore power fail. It can not be used to supplement the propane furnace. My understanding is that it can not be used, even in the smallest version, on a 15 amp circuit. Those features caused me to remove it from my "want" list.
Harold has a lot of experience with installing the "cheap heat" system, so he can tell you how many hours it takes to install it.
That said, the system may meet the needs of most RV's, in the highest wattage version, if they have access to a true 50 amp pedestal.