I use a mold release made by chem-trend. The stuff is usually used on injection or rotational molds to keep the molten plastic from sticking to the sides until it cools and then allows for easy release. It obviously stands up under great temperature and pressure variations and lasts for about 400 cycles. Unfortunately I don't know how long it lasts on a dish because I have only sprayed on one coat since May of last year and it still seems to be working well given that Western Washington gets more than its fair share of rain but little snow.
Okay, I'll confess. I already tried car wax on my dish this summer. My primestar dish was used, slightly stained from storage and the surface looked a little bleached out in places. I had just finished waxing the car and the wax said it was also good on fiberglass surfaces. I used turtle paste wax on the dish. The stains disappeared, the surface looked almost new and the coloration was even...for about 15 minutes. I didn't take into account the pebbled surface of the dish. The only way I could find to get to the wax residue in the textured surface was to use a toothbrush. It takes about an hour of non-stop toothbrushing for a Primestar dish. I stuck the toothbrush in the dish mount as a reminder not to do it again.