No need to sand the grill, in fact the P-Dip is much easier to remove if it's applied to a glossy surface. Be sure to clean the grill w/ soapy water, and bug tar remover or goo-gone if there's stuff that can't be removed w/ just soapy water. Then rub down clean grill w/ rubbing alcohol, let dry thoroughly and shoot the Dip. You just want to do multilple light coats rather than heavy coats, and be sure to turn the can upside down and spray til it's spraying clear, otherwise the nozzle clogs up while you're waiting for the last coat to dry. Also it's best if you apply the next coat quickly while it's still tacky, no need to wait the 45 minutes (like the can says) between coats, just 5 minutes is fine. I've done P-Dip grill, rear trunk chrome & my indoor brass fireplace screen doors.

As far as the "haters", no hate here, it's just a fact that paint & vinyl looks much more OEM (if it's done properly). P-Dip is easy to apply and does give a decent look, but the rubbery grainy texture, and the difficulty to clean (compared to the smooth finish of paint/vinyl) makes it less desirable IMO/ & IME.