Here's a trick I learned a long time ago, when you get to your dive location purchase a large plastic tub. They usually cost about 8 or 9 bucks. Take it on board with your camera in it.
I just explain to the crew that I want my camera and strobes in their own tub because of their size. If it is a small boat, I sometimes call ahead and tell them my plan to bring on board my own tub. At the end of the trip, I usually leave the tub for the boat. There is always a use for another tub on every boat.
Holding your camera on your lap or having a crew member stash it is probably more dangerous than leaving it in the dunk tank. Personally, I want my camera in water, which is a great shock absorber. On a lot of boats, the dunk tank is actually big enough and sturdy enough to protect your camera gear, even with other cameras bouncing around in there. But that is not always the case hence my bringing a personal tub on board.
Remember, underwater cameras should be reasonably robust. I hear divers say they are worried about their "delicate" camera equipment. If it's delicate, you really should not be diving with it, right? For the most part, underwater camera gear can take quite a bit of abuse. I have never seen any camera housing spring a leak in a rinse bucket.
Jeff