I'd like to build some raised beds for a vegetable garden this spring. In an ideal world, my local BORG would sell nice, dimensional redwood and I could bung them together out of 4x4s and 2x6s like everyone else. Unfortunately, my local BORG doesn't stock dimensional redwood. I don't want to use PT lumber, because I'm worried the various nasty chemicals and salts could leech into the soil and I plan on eating what comes out of the garden. That started me thinking about Trex. Plastic seems inert, and it is meant to be outside. Anyone see a downside in using it for raised beds? I know it is kind of flexy, so I'd need to put in a lot of supports to keep it from bulging... So they make some kind of 4x4 equivalent for Trex?