Some follow on questions.
I was planning on using oak that is readily available at Lowes. I Oak an acceptable material ?
My cabin top has a significant arc. I measured more than a six in difference between the height of the center to the edges. I was therefore planning to use 2 inch wide by 1/4 inch thick planks so they can easily be bent into position.
I was thinking I would need to install two of the 1/4 in planks to get the added stiffness I was looking for.
Should the two planks be installed at the same time, or should the epoxy be allowed to harden between plank installation ?
Let me answer these in a slightly roundabout way.
Think of an I beam for a minute. It has two flat straps (top and bottom) separated by a thin middle stem, but it's as strong as a solid beam. For your deck reinforcement that means you'd get stiffness by taking a second layer of glass, and separating it from the main deck.
Boat builders use balsa wood for this, because in that configuration the middle part doesn't actually provide the bending stiffness.
For your deck this means you could suitable pieces of any wood that's bendy enough to follow the curve of the deck and still get the deck to be stiffer - if you cover the wood with 2-3 layers of glass, this would work even if you'd use only a single piece.
Or, you could dispense with the wood entirely and use foam or air. 4"x1/2" should give you quite a nice foam blank. I think that you'd find that almost any combination of a few layers of glass, cloth and mat alternating would end up strong enough, although you could run a strip of unidirectional glass along the underside of the foam.
Whatever you do, each layer of glass gets to be wider than the next so you end up with a gradual increase in thickness. You also need to round all edges and "fillet" the transition between foam and deck so there are no sharp curves.
"Air" would mean a cardboard tube from paper towels or gift wrap. Sliced open to form a U. Well-coated with epoxy it will not rot later, and you use it like a foam blank.
Of course, you could simply glue some wood. In that case, you should know that red oak is not particularly rot-proof, and that's what your supplier will have. You would want to coat it in epoxy (all six sides!) after making sure it's well dried.
Traditional wooden-boat building would steam planks to make them conform, but that's tricky if you'd like them nicely dry for epoxy sealing.
The strength in your approach comes from using multiple layers of wood.
Until the glue cures they can slide against each other while they bend to conform to the curve. Afterwards the glue locks them into that shape. If you want to be fancy, you'd make them different width, so you get something that looks like an inverted step-pyramid. That makes for a more gradual transition between unsupported and supported parts of the deck.
You can do that with thin planks of oak, but I suspect the advantage of using that material will be limited. A/A exterior plywood (1/4") or marine plywood would do as well.
Adding each plank at a time, letting the glue cure, then covering the underside and sides in epoxy and gluing the next piece on would work fine. Or you could assemble the stack and glue it in one sitting. That should work as long as you have strong enough supports to force the whole stack into the desired curve (before the glue hardens, the stack is less strong). The latter would work best, I think, if the wood you use was something initially not very stiff (like plywood).
I'd probably go with the divide and conquer approach, unless you're experienced working with epoxy (and comfortable working under the time constraint of getting everything in place before the epoxy "kicks").
Make sure you cover all sides of the wood to seal out moisture and then cover any exposed epoxy with some paint for UV protection - over the decades of remaining lifetime for your boat, even the underside of your cuddy would get quite a bit of reflected UV.
If you use the glue out of the cartridge as I suggested, you won't have any hassles in getting the proportions right or having to mix more than you might need. However, each time you take a break in your work long enough for epoxy to cure, you'd need to get a new self-mixing tip - make sure to get a few.