If you purchase propane by the gallon or lb. the cost is the same. If your exchanging bottles, you are paying way too much for your propane. You already had thhe 30 lb tank, so, unless you traded you paid additional for the 20 lb tanks. Also, you will be refilling much more often with the smaller tanks. Should I assume you don't use much propane so that is not an issue? If it works for you, then I'm happy you saved the weight.
2011 Toyota Tundra double cab