Pretty nerve wracking running a sub "in the wild" the first few times. Looks good and major hurdle, everything dry so far. On a big boat like that do you have the propellors reversing to help turning? If not Kevin McLeod of KMc Designs has a Throttle Jockey you might want to look into.
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.