The Stovebolt Site Forums The Shop Area Interiors Hole filler suggestions, please.

Here is a couple of links for rivet nut kits.

https://www.harborfreight.com/45-piece-threaded-insert-riveter-kit-1210.html

https://www.amazon.com/dp/B003TODXQ...d_r=60afcccf-921f-4875-8591-a6bb5f285e95

If you only plan on doing a few holes, you can buy only the rivet nut inserts you need and use a bolt, nut and a washer to install the rivet nuts (don’t use any bolt or screw you plan on using to bolt on your door panel). Thread the nut on the bolt, then the washer and thread them into the rivet nut insert so the bolt just pokes thru the insert. Run the nut down until the nut and washer touch the insert. Install the insert into the hole (you’ll need to drill out the hole to match the OD of the insert) and using two wrenches tighten the nut while you hold back on the bolt until the insert cinches up on the sheet metal. A bit of oil on the nut and washer will help.

This process is slow but effective. The rivet nut installation tool is much faster and if you anticipate more fastener issues, would be the way to go.