I've also thought about using a weather proof housing, but since the boat is close to the house, I'll probably just install a camera inside the patio for overall monitoring. I haven't received the cameras yet, but I reviewed the online documentation and seem to remember a warning about exterior installations. Apparently, a bright light source (lightning?) can damage the picture quality.
I'm not too concerned about dead batteries, but a 110 outage is a definite possibility. Do you see any problems powering the cameras through an inverter.