I have removed all the rigid foam from inside the rear trunk lid trailing edge rib, in order to repair rust. I would like to replace the foam since it adds rigidity and connects the rib (which hosts the trunk latch mount) to the outer skin. Any recommendations on materials and process?

Don't put it back. The foam trapped moisture, and that caused the rust out issues in those areas.

I hear you, Clay, but the inner rib--with the trunk latch mount--seems too flexible without some additional support.

I'm still torn about the foam - especially the deep cavity by the tail lights. I can see how it promotes rust after it fails (not unlike undercoat) but worry about leaving those tail section open to fill with mud.

Although this article is written for more modern vehicles in mind, it still might be helpful.

https://www.bodyshopbusiness.com/auto-foam-...-misunderstood/

The thread title looks like it's about filling tooth cavities with foam!

Had same thought about cavity filler (rubber and the foam) at the back of the rear fenders, but would rather have some wet muck that dries into fine dust in those corners than put foam covered by rubber (or whatever that stuff was...), which definitely promoted rust in my car.

Suspect there's a fine dust/grit up there now from the few times I've driven my 914 in the rain since we repainted it, and am not worried about it. I'm guessing the Germans were worried about a salty slurry of snow and ice getting in there and staying wet through the winter back when 914s were used as daily cars.

Not sure what to say about the trunk lid cavity foam. Can see the point about rigidity. Wonder if there isn't something better now? Maybe not foam, but some sort of spray-in rubber?

I wonder about treating it all with Eastwood's cavity spray really thoroughly and then using the foam. One consideration is that your 914 will probably never see the exposure it got, pre restoration.

That said, trapping moisture is always a concern.

I'm just getting to this part in my project. I trimmed the foam pieces I took out to about half the size, and was thinking of putting them back in and brushing seam sealer over the ends. It's so hard to see up in that area and I'm a litttle worried about it getting packed with road debris and rusting. This would at least block off the most remote part of it!

I have 3 miles of dirt road between my garage and the nearest pavement, so there's that to think about.

Anybody tried this, from 3M?

https://www.3m.com/3M/en_US/company-us/all-...4025&rt=rud