There is not a lot of things unique about an Amel SSB installation over other boats, but I have a couple of comments on things to consider. I did not do the installation on our boat, it come with. So I have no pride of invention, just reporting what works.
We have the long whip antenna mounted on the starboard quarter. The base plate was mounted on deck and the support was on the rail When we installed the arch, we moved the base to the transom and the brace to the arch. It works well either way.
On our boat the antenna tuner was mounted on the shelf in the aft deck locker. If I was doing it over, I'd mount the tuner in a cabinet inside the aft cabin. Icom tuners are rated as waterproof, but keeping them rigorously dry is a better plan. and an extra foot or two of lead wire would not be a significant performance issue. If you want to use the rigging as the antenna, it gets a bit more complex, but still doable, and the physical arrangement will be different.
You'll need a 24 -> 12 volt convertor that is capable of holding the voltage at 13.4 volts at the full rated power draw of the radio if you want the best transmit performance. That's a lot. 40 Amps if I remember right.
If you are installing an 802, using the triatic stay as the DSC antenna has a lot to recommend it.
There is a lot of black magic on antenna installations. You'll get a lot a VERY conflicting advice, and everybody will claim to know best. I am not an antenna expert, but it seems to me copying an installation that works well is a good idea.