Hi Roland,

Sorry missed your question of a month ago. No harm because I haven't a good answer anyway. You asked if the dash might need to come out or whether something might need some welding.

The 245 in my example above is not a car for show in any state, or maybe I would have done more to protect the interior beyond throwing up an old sheet. And, of course, if any welding were to be done, the protection would need to be more fireproof than a sheet used for a painting drop cloth.

You suggest TIG (tungsten inert gas) with which I only have school experience. I think that might work well for adding the filler material to a lot of cleaned-up rust holes without sacrificing the strength of the surrounding good metal. I know I was not very good at it, mostly due to my eyesight and ability to keep the arc length steady, way too often back to the grinder to re-shape the electrode. Could have used weeks of practice.

As a practical matter in my car, if holes needed filling, I might try fiberglass and resin. I've used that method before in the rocker panels and been surprised at how well it survived years later. But, again, it was OK painted flat and better looking than the rust at 50 paces.
--
Art Benstein near Baltimore

Those who race through life finish first. (Darrel Hunsbedt)