My middle plastic piece (stock skid 2) has two threaded inserts at the rear that look like they line up with the front part of skid three and I bet the rear bolt holes on the skid 3 line up with the captive nuts located on either side of the cross member. In retrospect I should have tried this...
I think the prior comment about the third factory cover having an adverse effect on NVH is probably the reason NA didn’t get that cover. I’m getting a bit more exhaust drone now that my skids extend further back than previously.
A while back I was looking at the parts diagrams for ROW 100 series trucks and on most there are three skids with the third being a plastic skid to the rear of middle one we all typically have. Further, the Toyota skids actually appear to make a better seal around the perimeter of the frame...