How do you clean yours?

Muc-off, it's the best thing for everything. Cleans wheels, door shuts, engine bays, plastic trim, tyres, everything. Available everywhere as well.

For a "bulk buy" type product through, Megiuar's All-Pupose Cleaner is more or less the same stuff except it smells like Parma Violets...

Obviously niether will shift really stubborn stuff, but Gunk's all you need for that.