[EricH]

Put the bolts in the bumper and lock their heads down. Then put the bolts through holes in the frame (making sure that you have enough room to tighten the nuts). Tighten nuts on..wing nuts reportedly work well. Putting T-nuts in the plywood might not work as well, especially if they fall out.

Also, mark which bumper section goes where and in which orientation. This will help speed up the process, as you no longer have to put it in, only to find that it is crooked or should have gone elsewhere.