CCF:

Thanks for the tip on nylon bolts. I'll use that in the future, as they can be a bummer to get started.

This one I'm sure of, though. I stuck the screw all the way through the hole in the outer panels (till it bottomed), and compared the length sticking out to the length required to reach the blind nut in the inner panels, and they are identical. Needs another 1/4 to 1/2 inch to do the job.