Just because you take a 20# tank to the exchange, doesn't mean you have to keep going to the exchange. When my 20# tank expired ( for gas grill), I exchanged it and then refilled it until it expired. Around here, it is cheaper to buy a new 20# tank than to have it re-certified. I did swap out my 30# tanks for 20# tanks in my trailer to 1) save a little hitch weight, 2) make it easier to carry when I take the tank out when I am camping and hook my grills and stuff to it, 3) use the 30# tank at home for the gas grill (use more gas at home grilling than camping)
