Thank you all for your comments:
Marc U
I think your 5mm frame is going to buckle sideways between the stiffener attach points, and that was with epoxied joint which would add more stiffness than lashed. That is what happened to me on a 6mm frame (not okume). If you want lighter stiffeners, you might try laminating epoxy/ glass to the inside and outside surface of the stiffener (not talking about gunwales). You could also make the stiffeners like an I-beam. In my own boats, I added a lot of weight in the cockpit seating platform - for me I'd attack that first. The large ply forms at bow and stern are also probably much more than necessary. Last, I've always been interested in Bill Hamm's method of light dacron and glass/ epoxy, but never felt I understood what the weight benefit actually was.
I-beam is worth testing, use it where you need a hole in the frame for feet etc.
Splitting the cloth weight between Dacron and glass: my thought is that heat-shrunk Dacron gives a tight skin as a foundation for the stronger epoxy-imbedded glass which otherwise would not get tight applied alone. Stiffer and/or lighter than just Dacron. Is that right, Bill? I can buy 1 sq m pieces of glass cloth of different weights and make test panels of them with 3.7oz aircraft Dacron on frames, weigh the finished skins, and bash them with various objects. Then make my decision.
Bill H
There very well could be a variation of the two methods. Using steam bent frames and rigid connections. I've been planning on doing that to gain better interior room in a SOF.
Maybe steambent ribs in the cockpit part, ply frames and stems with lightening holes at the front and back of the cockpit and elsewhere. Make watertight bulkheads by covering frames with 3.7 oz aircraft Dacron, seal it. Leave little flaps between the longitudinals to glue onto the skin later. Did this on my SOF Bufflehead sailing canoe, worked fine. Put 8” diam. plastic hatches into the deck skin for ventilation.
Rich W
Finally, both my boats came in at 28 lbs using cedar stringers and 1/2" plywood frames and 9 oz nylon with Corey's goop.
Maybe the old lotus 7 story fits. Remove tubes till frame collapses and then put that tube back in. I've always felt that SOF kayaks and lotus 7 s shared a lot of their DNA.
28lbs sounds good to aim for. Loved the Lotus 7. I looked a bit more at Geodesic Airolite construction and comments on it. Someone, maybe Marc on Wooden Boat forum, commented that it is hard to get the kevlar roving geodesic stiffeners really tight so they actually work, and with a thicker skin, not necessary for counteracting torsion and bending.

Et M
I did measure the weights of 1m of 20x20mm pine vs 1m of 20mm diameter alu tubing at a big hardware store. They weighed the same. So I would have to go down a size of tubing to save weight. But I hate working with metal. Can’t see myself doing what George did.

I'll post again after I have done something.
Peter