I used rivnuts (10-32 I think) but bought the rivnuts made for plastic and fiberglass. They expand much larger and seem to hold fine. Also used them for the waterfall.
I have used the 10-32 rivnuts for the dash. The inside panel is thick and hard to shape to the inside door. I'll work on it tomorrow and use the #8 screws FFR provided. If they pull out I'll just use the same mounting holes for the rixnuts for plastic.
'33 Hot Rod Chassis #1118, Gen 2, hard top, bike fenders, AC, electric steering. BluePrint Engines Chevy 383 Fuel Injected with the 700R4 transmission 8.8" rear 3.55.