I sealed up the box and all openings completely with a bit of silicone. It is completely watertight, so no worries about corrosion
. I do plan on adding some dielectric grease to the external connectors when I hook up the wires on the boat to prevent corrosion
I hooked it up at home, and it was plenty loud with a pair of sony home theater speakers, but did begin to distort when pushed really hard, as expected (but it was louder than a comfortable volume in our living room anyway - you had to shout to be heard.). This was with an 18V source, drawing .2 amps according to my multimeter. With the more efficient speakers I have on the boat, it should do very well (enough to blast you out of the cabin).
It also produced next to no heat (amp chip didn't even get warm playing for 15 minutes). The amp doesn't even require a heat sink as it is so efficient and fairly low power
I'm happy with the little project!