I'm going to start a repair on the fender of my daily driver, and will need to drive in rainy weather while the repair is in-progress. If I'm shaping filler and need to stop for a day or two, how can I seal it from the elements so I can drive around until I get a chance to resume the repair?

spray some acrylic on it and then sand it off when you need to continue. primer, colour, clear whatever you have lying around. It wont protect it forever though so dont dawdle with repair.

spray some acrylic on it and then sand it off when you need to continue. primer, colour, clear whatever you have lying around. It wont protect it forever though so dont dawdle with repair.

ti286 wrote: how can I seal it from the elements so I can drive around until I get a chance to resume the repair?

That's not a good way but if you have too, you have too.
I would epoxy prime the area before starting the bondo,
that would keep you from rusting. After the bondo, whatever you
do don't let it get wet,it's a sponge that will soak up water and any
moisture covered with paint will come back to bite you.
When you finish bondo sanding you'd be better off putting an epoxy primer over that temporarilly, it will waterproof it better than a 2k primer
although a 2k would probably work well enough too, it would
be my second choice, being much better than nothing.