Thats what i was thinking but probably need to be sure before you drill some holes below the water line!!

3M 5200.... That's what the swim platform on my Baja was mounted with (along with bolts), but when teh bolts were out, it still just about didnt' come off.

My shop is picking up the Shadow-Casters. Should be available in a few weeks.

The install instructions for the Shadow Casters specifically states to use regular silcone and NOT to use 5200.

Meant to say 4200. I don't trust normal silicone to seal up an underwater hole.