Questions: self drilling/ tapping screws for chassis work

If exposed to weather, I would also think about using stainless steel if they may ever need to come out again. Plain steel screws will rust to almost any material, even fiberglass. When I replaced taillights and running lights on my '90 Western Wilderness TC I needed in excess of 30 screws. I had already spent more than $150 on lights I wasn't going to scimp on fasteners. I just bought a box of them.