Pretty common story but wondering if there is something I can do to maintain structure.

1985 245 with lots of rust. None on major frame lower body components but there is progressive erosion of metal around lower edge rear cargo compartment passenger side window. It has gotten to the point that the rubber molding holding in the window is almost hanging in air along about 3 inches towards the back.

I am looking for structual integrity not cosmetics. Any suggestions for building up the rusted body part so the window doesn't just "fall out". Will the window need to be removed and the panel replaced with donor metal? Fiberglass fix?

I know that the rust will just continue and that the car will eventually die of that condition however I would like to get a few more years out of the car since mechanically it is very strong.

Thanks for any suggestions

Howard