Installing metal roofing directly on to boat house shingles

I apologize if my question has been addressed previously, but given the type of structure to be re-roofed (an open air dock / boat house roof rather than an occupied structure), I thought I would start a new thread. The shingles on my lake boat house roof are approximately 20 - 25 years old, and many were blown off as a result of Hurricane Michael (I'm in N FL). Despite the missing and / or not great condition of the old shingles, the decking is otherwise in pretty good shape and the roof does not leak. Since my particular situation does not involve a climate controlled living space with attic, insulation, etc., and given the hassle of trying to match and replace the missing shingles on a piece meal basis, I was thinking of just installing roofing panels directly on top of the existing shingled roof. This would include screwing the panels right into the current decking and / or trusses. I also do NOT plan to install any underlayment over the old shingles, or to install 1 x 4's that the roofing panels would be screwed to. Given the type of structure involved, is this installation plan acceptable? If not, what should I do differently?