Good luck using any kind of "nutserts" in that thin aluminum, as they just don't hold well.
Install 1/4 x 1 aluminum flatbar 3" long near the corners, and behind the siderails held in place by an aluminum pop rivet 1/2 inch from each end.
Then drill and tap 1/4-20 NC the siderail thru the 3 inch long flat bar.
This gives nearly 3/8 total thread that will not strip out when using the 1/4-20 plastic knurled knobs found at most hardware stores.
I have detailed pics that I have posted in the past, but way to difficult to post anymore.
