Not sure whatever came from this but I have a couple of ideas.
Obviously running through water tight pvc will be needed, as far as the box holding the camera you could do a landscaping box, and instead of the plastic top you could use cut plexiglass and obviously lots of good quality caulk with screwing it in. pressure won't be much of an issue being only 4ft down. Just making sure it's nice and water tight... The landscaping box has a rubber seal in addition to the screw holes all around it and the holes for pvc conduit.
Here's the tricky part, you want to be able to use IR through the water right?
The way to do this is basically replicate what a dome does with its IR's and the round foam ring separating the camera lens to keep the ir out of it.
You can do this by splitting the box in half in a sense. Camera with no IR or IR OFF, and then a board with foam on top that the plexi lays on and on the other side of the board can be a cheap
IR light...
This would seperate the two and not give you any IR reflection in the glass.
I'll try drawing my idea but im no artist.
Edit: Ya know, I just thought about this by why not just put an underwater light on the dock... Just like the ones installed on the back of the boats for good looks? Then you wouldn't need your IR... AND the light would be right where you want it at the prop... This is probably the better Idea by a long shot!
