I have been at parks where the majority of sites are permanent or seasonal. People are there for months at a time. They have 'big tanks' setup next to their RV/Mobile home. A truck comes from town every few days to fill up those that ordered such. They will NOT fill up anyones portable small tanks. Again, this is for mostly mobile home parks that allow some RV overnighters.
I always check tanks before leaving on a trip and call ahead to see if RV park will fill tanks. If I fill them locally I usually tank the tanks to Costco where it is VERY cheap to fill. Only a few Costco's have propane around here.