I was talking to my LBHS owner today and he mentioned something that I'd never considered. I'm going all-grain soon and said that I'd be converting a cooler to use as a mash tun. He said that's a fine way to go, but that after a certain number of batches (12-15) the plastic within the cooler will warp. So there's only a finite number of batches I can do with this equipment (he was advocating just getting a keggle and going with stainless from the beginning).
Have any of you had a problem with this? If so, how long does the cooler last, and what are the difficulties associated with mashing in a warped cooler? This seems like the most common method when going all-grain, but I've never heard of the cooler having a short lifespan before.