[Festus2]

If you can easily remove your batteries, I would take them out and store them in a warmer area, put a trickle charger on them and make sure you top them up with water from time to time. As you indicated, you can leave them in the RV and use the converter to charge them up but with the freezing temps there, you might want to take them inside.
Your propane tanks are fine - if you want to top them off that would work too.
The breathable covers you see wont keep your RV any warmer and there are a wide variety of opinions about the pros and cons of covering. I think the majority of people avoid using covers for a variety of reasons --- chaffing, billowing, marking up sides and top, etc. I think the jury is still out regarding the issue of to cover or not to cover and most people on here will most likely tell you to forget it and save your money.