The only thing i can come up with is to start with a long mitre on the edges, use a jig to cut a 45 degree dado on each corner, then inlay the edges/feet?
My concerns are:
- I can't use splines on the mitres, they'll be visible.
- I'll be cutting most of the mitre joint away, leaving very little glue surface.
- I'd have to glue in the feet/edges cross-grain, so the glue will probably fail with wood movement.
The upside is that this is an urn (i guess that's not an upside for everyone involved) so I'll be gluing the lid on, which should provide some extra stability.
Make the feet “ribs” protrude into the box, with a 45° rebated channel cut into each side that the side pieces slot into maybe? Have the foot detail just extend under the base to support it. That’s a lot of glue area even if the sides and base are thin, and you’d only lose a small part of the volume to the part protruding into the internal volume