Like J-MAN, I'm very happy with the GG Rubber Prep + Ultima TTGP combo for exterior plastic and rubber.
J-MAN- Yeah, IPA is good for cleaning away the "dead rubber". I never had any problems from using the GG Rubber Prep for it though, didn't dry things out or anything like that.
Oh, and you know the whole "petroleum distillates kill rubber!" thing? My experience has been different- I've been using a (non-staining, trim-friendly) wax on my Jag's exterior rubber since the mid-'80s. Still in showroom condition, no problems at all after nearly 30 years of this treatment. I do use a wipe-on-wipe-off approach though.