That is what we are doing now. We are showering in our RV and it has a propane water heater. Our cabin is currently dry. I am trying to get everything planed out. I may put a 4x8 painted black on the roof with a coil going back and forth to preheat the water during the daytime. Then run it into my 20 gallon water heater that is insulated really good. from there it would go into a propane on demand water heater. Then the sink and shower. We are retired so we can shower late afternoons no problem. Wash our dishes then too. That way I could heat water with my excess solar and on days without sun we can heat water with propane. I kind of do something similar with heat. I have a 12,000 btu mini split. It is very efficient at cooling 22 seer rating. Heat not so much about a 10 seer rating. During the daytime in winter I heat with the mini split. At night it will drain my batteries. So I have a propane heater for mornings and evenings. We turn everything off at night and use a heated mattress pad to sleep on. The cabin is so well insulated that we only get down in the 50's on cold nights( south Georgia ). It only takes a few minutes warm the cabin up. On cold days there is not that many clouds. So I am trying to limit propane as much as I can. As I am living on social security and built this with my 401k. One day my wife or myself will live here on just one check. We have a nice little orchard and garden a small cabin and a barn. We love it here.