We get plenty of moss here in Cornwall due to being damp most of the year, usually starts sprouting around the window rubbers and trim. All I ever do is use my karcher pressure wash which always shifts it, surprising how much crap builds up in the most unlikely places.
once the moss is cleaned off ..
this product works well to protect rubber / vinyl / plastic ..
( e.g. to prevent the black bumpers from fading to grey .. etc .. )
can't imagine moss would want to take to it either ..