Corner glue clamps
These corner pieces hold it together while the glue dries. Either rubber bands or elastic cord provides tension. Box / finger joints don't require much pressure, just keep them snugged up tight for a while.
These were 3d Resin printed. After some trial and error, I figured out what orientation works and what don't... The software's auto-supports were a mess so I added the necessary support structure. Those little pieces can easily be removed before post-cure, while still soft..
Scaling is entirely possible. These ~40mm cubes are about as big as my build plate will allow.. I recall they use about 10ml of resin each.