Bill Epstein Messages: 1088 Registered: May 2009 Location: Smoky Mts. USA
Illuminati (2nd Degree)
Get a 3/8 rabbett bit for your router or a dado set for the table saw and make the entire back an access. Rout or dado 3/8x3/8 rabbets on both the rear panel and the rear opening so one fits into the other, Then apply a single strand of rope caulk all the way around. Screw it down. Lots of test cuts on scrap until it's just right.