Do you think the fiberglass/epoxy would work well over 5” edge glued cedar board/planks?
Since you're only sealing one side, I'd be concerned that the boards would still move with changes in humidity which would cause delamination.
but the extra labor to make the strips seems daunting.
I built a cedar strip canoe. I "gang-ripped" the strips (two at a time, with two blades, set 1/4" apart with washers) on a cheap table saw. It wasn't that big of a deal. It would have taken twice as long with one blade, but still no biggie.

From time to time here, I see folks that are newbies with little or no woodworking experience come up with experimental ideas that end in a camper that doesn't work out. I suggest using proven methods for your first.

Tony