Thanx all for the really helpful hints. Since the cabinets are made of HDF and I plan on painting them, I'm going to router, seal and sand, seal and sand, seal, etc, all the exposed edges with West Systems epoxy and filler. That should take care of akhilesh's suggestion. I still think they'll probably need a horizontal brace in the horn mouth as well. There are 2 corners per cabinet that are hollow and probably should be filled. I could drill a small hole and fill them with something. Any suggestions?