I'm leary of the 'H' channels. They require very carefull fitting, I'm uncertain of their strength, and çI think they would leave an unsightly bump.

Let me suggest instead that you make the deck and hull edges match. Before joining those parts, build a lip on the inside of the hull. Make this about an inch high. Use a material which is about two inches wide. Half of this will bond to the inside of the hull, and the rest will come above the joint line.

You can use carbon, or fiberglass for this. That gives you the strength in the inside bond.

Behind this lip, glue on a strip of pine. It doesn't need to be planed, or knot-free. A little epoxy and some clamps will work to hold it in place.

To assemble the boat, coat the lip with a thickened batch of epoxy. Then drop the deck onto the hull. The lip will keep things aligned, but probably there will be areas which need some attention. Use pan-head sheetmetal screws, or roundhead woodscrews to pull things together. Drill a pilot hole and drive in the screw. The woodstrip on the inside will give the screw something to bite into.

Once the resin cures your deck and hull will be solidly joined. Remove the screws, plug the holes with some chopped fibers and resin. You'll be putting a strip of glass or carbonfiber over the outside of the hull-deck seam, and that will completely hide any trace of the screw holes.

If that wood strip inside should rot away over time it won't affect the integrity of your boat.

If you build the boat over a solid block of plastic foam--sculpted to shape--you leave the foam inside and make a one-piece shell around it from your carbon fiber and resin. No joint between deck and hull to deal with. If the weight of the entombed foam bothers you, use a cheap styrene foam.Wait until you resin has cured completely. Drill a hole at one end, pour in some acetone--it doesn't take much--and the styrene will dissolve. Pour out the solution, let the fumes evaporate, and plug the hole.
Hope this helps
PGJ