Positive ground solar installations can and are used on some boats. One point is to make sure the panels are isolated from any metal part of the boat. This can be accomplished with inert (plastic or grp) blocks between mounting points. Here is a link to a pdf regarding positive ground wiring rfrom Morningstar.
Steve Dashew's installation on Windhorse is positive ground. Here is a link to an explanation of his system, with comments.
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