temporary body work

If the window is leaking I would pull it out and fix it. That rusty bare spot doesn't look hard to fix. (at least from the picture) Im not a body guy and I long ago gave up on building super pretty cars. I would grind as much of the rust clean as I could and then use naval jelly or something to treat the rest. Maybe even use a spot blaster to get the rust out of the pits. Weld a patch in teh hole. Cover with a thin layer of short hair fiberglass,then plastic. I like UPOL urethane filler primer but (body guys will hate this) If it is going to stay exposed for long I would use rustoleum rusty metal primer catalyzed with majic hardener. This stuff is tough!