Another vote for Zaino here. I have to park outside (offstreet at least, thankfully). I can't do waxing 1 day a month, so the 6 months a few layers of Zaino will last does the trick for me.
You can always re-apply Zaino CS midway through your 6-month cycle after a wash as well. Keeps the other stuff on.
2015 SO/SO MT M3 :: Exec : Lighting : Adaptive : HK : CF trim : Full leather : DAP : Black 19's : sunshade
Crystalline tint 40%/70% on windshield : M performance mirrors, spoiler, splitters : Status Gruppe CF lip : RKP diffuser : Fully dechromed
Bavsound Stage 1 : V1 Savvy hardwired : Self-coded