I installed a 3mmply
: deck on an 11" radius beam glassed with 4oz on the underside with a
: teeny stringer (3/16"x1/4"). The top was glassed with 6oz.
: Without a bulkhead I could stand on the deck with no problem.

Thanks Lee and all, that is reasuring. I had overlooked the option of glassing flat then bending and installing onto the hull before the epoxy had fully cured, I think I will try it, sounds easier than trying to duplicate the camber off of the boat.
Maybe a mix of both, bow the sheet a little by placing blocks under the panel on the sides and clamping it to the worktable in the center, glass, wait 8 hrs and install.