I'm one of those funny gits who doesnt like making mistakes.....
That's OK.
In that caseI would suggest you make the sides just like a normal brood box.
The ends can be cut a lttle longer than needed and dropped into routed slots in the sides.
A little more work, but a better construction than butt jointed boxes. The grooves can be deeper than actually required and can be filleted on one side, or both, to adjust the width if ever the width needs expanding slightly.
No need for glue in the joints as the box will remain square and strong using screws as fixings. It may be called 'belt and braces', but would avoid most of the costly panel rejection errors where butt joints are concerned. Even out-of-square pieces can easily be trued up, with no visible evidence of there ever having been a slight discrepancy with a saw or marking up.
Any end grain break-out will be covered up within the side panel grooves, so the boxes will last longer.
Simple precautions within the design, if you are not so confident with your cutting, can avoid a lot of small problems later.
RAB
