I have an old rutlands dovetail/box joint router jig that you can attach to a piece of wood.
The wood needs to be 2 1/4 inches wide and square, so it needs to be trued and then cut to width on the table saw.
I have a router bit for to cut a t slot so you can add clamps. I am planning to use this to make a guitar cabinet
Pic of the bits which might help