http://www.golehr.com/products.shtml#1
These seem to be a good idea. Propane doesn't go bad like gas and they claim one of those canisters is good for 2 hours. Thats probably a month's worth of use on our trimmer, and more than a 2 stroke trimmer will run for on one tank.
http://www.sears.com/shc/s/p_10153_12605_07179212000P?keyword=propane+trimmer
Sears picked them up, I'm going to buy one when we need a new trimmer.