Depends on the MOTORIZED antenna. Some won't even take a warm rain without getting messed up, and others SURVIVE no matter what.
RainX works well to protect the plastic and metal parts. Repair-Tape (a vinyl, self-sealing, non-adhesive tape) works very well to seal the coax and/or PL259s if you apply it correctly.
One of the most over-looked aspects is the bottom insulator. You can use RainX okay, but if you use car polish to protect it, chances are very good it will arc over especially in wet weather.