hello Tom,

Generally the boxes, assuming they're commercially produced, go together very easily and quickly.  I usually coat the mating edges with glue, then nail together the fingers of the joints.  Before it dries, I'll check the squareness of it either by measuring the diagonals, or with a carpenter's square.

If you need a jig for the frames, I have one you could borrow.

Good luck.

Allen Engle