The above picture shows the bottom view of the base assembly. The frame is routed inward 1/2" with a depth of 1/4". The 1/4" thick plywood is placed into this groove. Before installing the plywood, I ran a bead of wood glue along the outer perimeter and a bead of tub and tile adhesive caulk along the inner perimeter of the routed section. Any excess of these adhesives should be wiped off. This application will seal the base should there be an occasional spill. This same sealing process was applied when attaching the 3/4" thick frame. The plywood bottom is also held in place with size 6 X 5/8 flat wood screws. Use of any smaller size screw may not handle the insertion torque and thus the screw head will break off. The screws going to the ladder and perch post base attachments can also be seen in this view. The plywood bottom is also given three coats of polyurethane.