I'm still in the planning stages for a build also, and I was thinking along the same lines. Seems like it would be much cheaper than fabbing up all of the steel for some of the water table designs I've seen posted on here. You can also pick up some large plastic sprayer tanks for farm equipment (65-150gal) pretty reasonably at farm supply stores or farm auctions. I see no reason for something like that not to work? I've got a 65 gal sprayer tank that I use to water all of my trees during the summer.