Good idea. I'm planning something similar, but I have to wait a little because we are purchasing the house right now, so I don't have cash to invest.
It is generally a bad idea to only heat one room in the winter. I understand that you don't have tap water, but you have to pay attention on the walls too. If you don't heat every room, the walls will experience great stress and will degrade faster. Not to mention that your doors inside the house are way worse insulators that the walls themselves, so the cold rooms will affect your heated room too.
My advice is that heat those rooms too. They don't have to be that warm, but heat them too.
RE: I am thinking about maintaining my current rent with solar power (2022.02.10)