Hello Angelo & welcome to the OVNIClub !
I don't know if you can understand this thread : http://www.ovniclub.com/forum/blu-masse-t119.html
by using Babelfish or the Google translator ? it answers most of your questions.
In summary the way most SSB radios are mounted on Ovni yachts : the AT box is grounded /connected to the hull through a "high capacity" condenser or capacitor, which blocks DC current (hence preventing potential electrolysis issues), but not the AC current (HF in this case) so the radio and antenna work. Sometimes several capacitors are actually used, as they also function as filters.
The AT box reads for Automatic Antenna Tuner (e.g. AT 130 or 140 if you are using an ICOM SSB) and really helpful, especially if you are using an isolated backstay as the antenna. This AT box should be located as close as possible to the antenna.
This of course is valid for an Ovni aluminum boat (and most pleasure alu sailing boats in France whose hulls are totally isolated) using a bipolar electrical scheme. In this case the other solutions you quoted would be detrimental. However pls. note that not all aluminum boats have the same type of electrical system. As for some professionnal alu. boats (a legal requirement in some activities/countries) the hull is grounded and some of the solutions you listed may work.
Hope this helps.
Best wishes, Kevin