I have never fully come on board with aluminum and salt water. Unless it will be trailered. We work with ships' various hulls and decks. Things tend to go better if there are no engines or batteries. I have seen massive base metal waste due to improper use of anodes. It happens faster that rusting. It never sleeps. Use some stainless steel fasteners and reap the pleasure of bonding.

Then comes the joy of welding the stuff. The American Welding Society will tell you it is the easiest metal to weld. They have to be talking about melting temps only. It is the most prosity prone metal to weld... meaning lots of holes. We made money as consultants to the trawler industry to come in and troubleshoot their aluminum setups. They were having trouble getting it from being so brittle and manage to tensile strength too.

If you already know about these things, you are half way there.

Good luck.