Originally Posted by Toxophilite

So I got this cute little 1980 240D for a reasonable price cause I knew the floorboards needed fixing.
It has the typical rust through in the corner between the floorboards and the sides, making for lowspeed seatbelts and potential ejector seats.
I fixed one of these before using sheet metal lot's o' steel pop rivets and seam filler. It made a strong fix, not welding it's true, but strong.
I ground away as much rust as I could reach, treated everything with a German rust converter, primed it and then did the fix.

Anyway my question is..the evil undercoating.
Should I get rid of it below the area I'm fixing ,then clean it ,rust treat it, and paint it. That's my inclination

I've looked at those cool panels they have for fixing all the rust problem areas and I was tempted but I have all this nice old galvanized sheet metal .(it's free)

240Ds are cute..it's an auto, but I like a slow car, everybody drives way too fast, it's inefficient , dangerous, expensive and tickets are very costly!!