Patrick,
Regarding your amp question, I know that Kenwood offers a solution product that meets NMMA (National Marine Manufacture Association) recommended standards. Kenwood, I believe, has a range of products with various power outputs, however, not every dealer has access to them as as it isn't offered from Kenwood directly. There is an exclusive distributor for marine in the States who sells the "certified" product to certain retailers. It's not advertised on their site but rather the product is tweaked at the national distributor level to conform to marine application.
Also, I believe that MB Quart is either already shipping or is going to ship new amps that meet NMMA recommended standards.
I know that this is bias because of who I represent, but I would recommend at taking a look at the
www.wetsounds.com product because it was built with salt water and harsh marine environment in mind. With Injection Molding enclosures and stainless steele hardware, you won't experience negative reactions to salt and moisture.
Regardless of the direction you choose, speakers that is, I wish you the best on your hunt for a good amp. If I get wind of any new developments I will post them for everyone's knowledge.
Dale