Hi Jay,
i make display cases and carry boxes (the glass replaced with ply) by slotting 25mm square timber using a table saw.
Set the depth and I usually start the slot 10mm from the outer edge. I slot ALL the timber before cutting to length. Next cut to length and either have plain crossed ends or cut a 45' angle. It is usual to pass the timber at least twice over the blade to make the groove wide enough say 6mm for ply, as the saw blade may not be the required width.
For a case the whole is mounted on a base board, the glass slots home and is held in place with dabs of silica. The top is screwed on to give added support.
For a box, I slide ply in the grooves (made just bigger than the ply thickness to allow for the glue). The top or front, you decide, is left as a sliding fit so you can put the boat in.
Kimosubby