We're developing a cleaner we're calling EveryClean "Cleans Everything ". It's not ready yet but will be soon. For now best cleaner we've been able to find for that sort of thing is starbrite black streak remover.
The key is to use a stiff bristle nylon brush and any boat soap. Also if you want to add a layer of sealant to your Marine Mat we're bring on Starke Shield which repels stains.