Originally Posted by MarkH
Thanks, that's what I was beginning to think.
I did consider your suggestion of making the two aft pieces out of one piece of 12mm ply, but I was concerned that it might make it difficult to manoeuvre into place with the front triangular piece. If you think this wouldn't be a problem, I'll give it try though.
With the 310 you slot the aft two pieces together complete with the side strips of aluminium before you fit them into the deflated boat, so two pieces fitted together and rigid, or one complete piece - it makes no difference.
The fitting is made easy because of the third bow section, slotting together as you fit it in the deflated boat, I think the bow piece will always have to be separate. You will need to get the way they connect correct as it sort of falls together as a hinge, just as the photos you posted above. I can take measurements if that helps.
I think the two aft pieces where made that way for easy storage onboard a sailing yacht. "Sibbing" wasn't really a thing back then.
Could still be a big piece in a car, depends on how you use it.
Let us know what you decide, I'd like to see pictures of what you achieve.