Just helped a crew of B C duck hunters put out hen tubes and wood duck boxes. Their wood duck boxes have a 4" round opening in the side near the bottom to make it easy to clean. Place a small square of plywood over it with short wood screws to cover when in use. (opposite corners seem to be all needed) I've helped put out others that have a part of the side panel that rotates at the middle to get cleaning access. It has a swivel lock that keeps it closed. It is a surprise when you open it and mice bail out down your arm. Found a small owl peering out at me from a box being cleaned; left him undisturbed.