The side panels fit on pretty easily, holes need to be cut to allow the wires out of the enclosure at the ends. Drill the hole then Demel on both he top and bottom locations.
(Top) 
(Bottom) 
The top tabs and openings match up and just needs a little extra push and that’s it. The second tab is pretty simple, I just lined up a screw driver to where the slot should be and punched it through with a hammer. The middle tab slot ended up just below where the side line gets greater in size. The bottom also lines up well and just needs a little extra push.
