Ummon,
I agree with you, looking at the cabinet from the side, it appears there is no shelf (I drew in that orange line).
If you had the same pieces of wood fastened to the sides of the CP as the cabinet, you could secure the sides with bolts. The bottom would be slightly more complicated. For strength, I would think you'd want the CP to extend over the inside front of the cab. If it did that, you could bolt it to a piece of wood and threaded anchors that was positioned similarly to the one on the TMNT. I wonder if there's a brace underneath the CP on the outside front of the cab as well?