I could be wrong, but waterproofing it may not be the best idea. They are water resistant just like your reciever, motor, and steering servo. So if you waterproofed it or not it wouldnt make a difference because all of your other electronics are still able to get wet. (meaning that it is not the weak link in the system)
I would think that by not waterproofing it, it would be allowed to "breathe" a little better. If they were intended to be all siliconed up, they would have came that way from the factory.
Ultimately your best bet is to keep it out of the water
Just my .02