First, ask around your RV park or town and see what they use to get good reception.
You could always go to WalMart and get a cheap TracFone. For 3 months, you can get 90 minutes for $20. When you get home, don't use it again. You'll loose any unused minutes but you can re-purchase minutes the next winter. It's cheap enough. Or use it at home until your minutes run out.
I'm not sure which is which but some are on the Verizon towers and some on AT&T. Since your Verizon doesn't work you'll probably have to get one using AT&T's towers.