Well, thanks all for the help on the rust patch (floorboard, 1987 745 GLE). I've cleaned it all up, added some anti-rust agent, and closed it temporarily (until I can get to the body shop this spring for real patching) with duct tape and a piece cut from a rubber floor mat. It won't be driven much at all - maybe one or two days a week around town - until March or April when I plan to have it ready as a daily driver. Question - when I finally close it up, what's the best spray-on undercoating to put on there? Thanks so much.
-Webb

Sweet!

I would say that an undercoating with a wax/oil base would be best as it is very durable and 'repairs' itself if scratched or compromised in some way.

In Britain we have a DIY product called 'Waxoyl' which is available as a thick liquid that you can spray into box sections, doors, etc. and a heavier type which is basically black underbody sealant with the 'Waxoyl' liquid added to it. It works very well at preventing new rust and retarding existing rust. I imagine that there are similar products available in the US, etc.

If you can get hold of the stuff that Volvo dealers use, even better :)
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