Refills are generally more cost effective. First you get more propane and 2nd it costs less per gallon.
There are always Places that can refill.. Google as follows Propane near ##### (The 5 digit zip code of the park)
Depending on where you are
Gas Stations
Hardware Stores
Campgrounds
Pilot/Flying-J
Propane Wholesalers (I like Parker's in Flint. MI. Carmichaels in Tekonsha MI and both the Ace Hardware (I think might be True Value) and the Tractor Supply next door in Seneca SC) to name but 3 places.
NOTE Carmichaels is hard to find for most folks. not for me.. (Farm I grew up on).