A tip that always helps me is to look for spot welds. That means there is another sheet of metal right behind it. Dont screw directly into a spot weld, just next to it. The screw will hold MUCH better than if you were to use a location with only one sheet of metal. Grind away the paint and use a star washer as mentioned above. I find that using a large self tapping screw (or a regular screw, but you have to pre-drill a hole) with a hex head works best. Something with deep teeth that can grab more metal. They have somethign called a 'thread-forming' screw that looks a bit triangular from the end, it presses threads into the sheet metal instead of cutting them which gives you a stronger hold.
"-@--------@--" 1990 SSE " Black Ice " 220,000+ kms, GX3, sunroof
16" Streetwear Diablo wheels | Blazer Fog Lamps | Silverstar 9005 low beams | Mesh Grille | STB | '94 Top end | Delco Type 2 Ignition | Blue interior LEDs | LED 3rd brake light | Auto-dimming rear view mirror | Pioneer DEH-P7600MP | Rockford 5 1/4 Components and 6x9s
Daily driver : '95 Buick Regal Custom | Blue under dash LEDs | Infinity 5 1/4 components | 8 Inch sub under dash | 12 inch Bazooka sub in trunk | Rockford 4 ch amp | Trunk mounted EQ | Pulsing trunk LEDs