[DanEC]

Lippy - I use 10-24 rivnuts. The countersinking is a good idea - I didn't think of that. I may countersink the transmission cover holes on the underside instead. But I do plan to use a 1/8 inch weatherstip seal too.

I also used rivnuts to fasten the top transmission cover to the footboxes up under the dash.

If you haven't already, I would bookmark McMaster Carr for lots of small parts, tools, hose, weatherstrip, rivets, rivnuts, washers, grommets - about anything you can think of. And they ship quickly.