We bought a new travel trailer last year that has twin 20 pound propane tanks. e camped about every 2-3 weeks last year after we bought it, and used a LOT of propane.
I took those 2 tanks and my spare to Tractor Supply to have them filled.
$70 for all 3! YIKES!!!!
The camper has sat since Christmas and we just took it out for the first time last weekend, so I haven't had to buy any for a while