The CG we are currently in (central Illinois) has about 20 sites they keep open for the winter. Even though they won't let you skirt around your RV they usually keep most of those 20 sites full all winter with full timers.
There are two different propane companies I have seen come through the park in the last week. They are setting up twin 100 pound propane bottles next to a few of the folks that are staying all winter. Talked to one of these customers and they said these companies provide the tanks and hook them up for you then you just call them during the winter when one gets empty and they come out and either fill it or replace it. The guy I talked to said they were actually pretty cheap.