While 30 pound tanks are a pain to refill, 20 pounders are much more convenient. You can simply stop at any Dollar General or one of hundreds of stores, and simply swap an empty for a full one. It's probably more cost efficient to buy 30 pounds at a time, vs. 20, but a whole lot less convenient.
Alternatively, since you are working out in the yard, simply run an extension cord with adapter out to the camper, plug in the camper's power cord and you'll have lights and can run a small electric heater too, saving your propane for other things, like the refrigerator.
2014 Coachmen Catalina 253RKS
2016 Summerland Mini 1750 RD
2012 F250 Lariat FX4 Crew Cab 6.2L