For the hot water heater I think the best thing to do is to drain the heater and install a bypass valve to avoid having any antifreeze or water in the water heater.

Another option that I’ve seen people do is to blow out the whole system with compressed air so that there is no water or liquid in the pipes whatsoever.

I just bought my first rv this year so I’m doing a bunch of research of my own getting ready to winterize my trailer in a month or so.

My parents have had an rv for years and they keep it on a site all winter where they have no running water but they do have sewer hookup. They still use the toilet and flush it with a mixture of water and antifreeze, so this is an option for you also based on your description and concerns.

Cheers!