Perhaps you should look into the finish modelers are using for modern subs since they have a rubber coating on them.
Might want to have a look around the SubCommittee forum to see what people are using and also do a google search on modern subs to see what they look like.
I would not go with rubber dip since it would be to thick and would not look realistic, if you wanted a actual rubber coating there is a spray for bumpers that is a thin rubbery type coating many prop builders use.
unless you plan to handle it a lot I would just go with regular paint.
Eric...