sanding in the rain

I suggest sanding with 60 or 80 grit to bare metal , 1 panel at a time and then using epoxy primer Say 2 coats, it's waterproof and will give you the "time" to get all the way around the car. It is more $$$ but Regular primer is pourous and you have to sand n re-prime if you leave it outdoors. A total waste of $ IMO

My .02

Eric