If you're using 3/4 ply and 1 1/2+ screws, it'll hold. Like the other guys said just remember to countersink first to avoid the plywood from splitting. Once you put the backs on the cabs, glue or no glue, those cabs aren't going anywhere except on the wall when you hang them.
Yep beautiful stuff. I think I saw $190 on that no. 238 or 239. More then I'd wanna pay for that one. I think I saw a 602 somewhere in those pics. *insert drooling emoji here.
Next time when I'm in KC I'll have to stop.