This weekend I've been redoing the sound system how I'd like and detailing the interior, it turns out the old amp was mounted with self tapping screws by the previous owner-I can feel them underneath the car. I took the screws out but how do I plug the holes while preventing rust? My first thought is to fill them with silicone but then if water gets underneath that I'm in trouble. The car is a daily driver all seasons and I plan on having it for a very long time so I'd like to do it right.

 

First I would remove any existing rust within those holes, then apply paint both inside and outside the holes. A spray on undercoat applied to underside and inside should permanently seal the area. This is the cheaper method, otherwise you are looking at welding the holes, grinding the area smooth and repainting/sealing the area.

 

Sounds like a good plan. I think I'll take it to a body shop just to get an estimate but I'll likely go the other route. Thanks! And do you have any recommendations for a spray on undercoat?

 

The body shop might offer a similar product to what I've listed, the prep work (cleaning dirt, oil, etc from area to be sealed is the key) and applying paint prior to sealing is the other key. This site has a whole myriad of products for prep, rust eliminator/surface prep and sealing. The other brand i would trust for this job is the 3M sealant.

http://www.eastwood.com/ew-textured-...html?reltype=3

 

You could pop-rivet the hole and under coat over it.

 

Nothing some bondo cant fix.