Yea, it'll probably sag, but I have a few options that I've thought up. Now they can be pulled out of the frame, so I wouldn't want anything permanent, but I can rig up some sort of bolt bracket system, either inside or on the front, so the top panel is bolted to the frame. The frame has two support 2x4s at 24" and 48" below and above each enclosure. Maybe I'll just go ahead and do it now, if I can think of exactly how I want to do it. Actually now that I type it out I think a good L bracket would work how I'm thinking.