I am building some wall hung cubes for underneath my TV out of walnut. What is the best way to attach these to the wall? Before, I did a solid back that is captured in a groove in the carcass (not sure if I should have done that or not) that seem to be working fine. I do not really want to waste all that wood for a back. Could I put a rail at the top and the bottom? If so, how do I fasten that to the carcass? I'm fairly new to all of this so all your help is appreciated.