Where I live, the RV parks and dealers outside of Austin will be more than happy to top off a propane tank.
However, in town, you will get excuses, "Please show me your DOT certification to possess a propane tank", stonewalling, "That propane pump is no longer in use" (while someone out there is filling a 30# bottle), or demands for me to sign a 250 gallon contract before someone will lift a finger.
Because of this, an Extend-A-Stay/Stay-A-While system is a must (cylinder exchanges are a lot easier to come by than getting them filled.) I also try to run as much as I can from electric unless boondocking... and when boondocking, I can carry in a cargo rack or on the hitch of a small cargo trailer two 20# cylinders that would more than last a weekend.