Rust repair

David09

I've an old 90 ford fiesta van which has corrosion on an arkward location on the rear quarter panel.

I know the car is utterly worthless and that it doesn't make economic sense to repair, but it's been in the family from new and was my own first car, many years ago.

I pulled it out of the shed to try make a start on tidying it up. I scratched and poked around at a rust blister and it crumbled and crumbled...

I'm looking for advice on how to go about repairing it in such a way that the rot won't spread away quietly behind the scenes when all is finished on the outside. I've ground the rusty section out and the only way I can see to fix it is to fabricate patches to weld in or else cut a matching chunk out of a scrapped car.
The bit I'm unsure about is how to seal the inside surfaces of the repair after it's fixed as it's a double-skinned panel with no access to the void behind it.

Here are the pics. Any advice is greatly appreciated...
(except that of shoving it from a high drop or dropping something heavy on top of it )

Buford T Justice

Before you weld in pieces to cover the holes you can spray the void with waxoyl to prevent more rust on the inside.

Also, the rust that you've ground down, either cut it out or get a rust treatment for it or else it'll start rusting again.

Hal1

That looks too far gone, cut it out and fab a new piece.