(Router) and or a (Bit) that would hollow out the inside of the Box Call and or the Slates, this would save alot of sanding. A (Bandsaw) would make the shape of the Box and the the Slates.
(Electric Belt Sander) would work well too.
Boy I better quit before your Wife gets on here a Cusses me <img src=icon_smile_big.gif border=0 align=middle>...BT