Garry,
I think you have found the answer
Thats whats so amazing about this website - Post a question, go off to sleep and when you wake up the next morning, great minds have been at work and theres your answer
Youre quite right, the two halves dont have to nest inside each other, its only for storage, and possibly also to be able to handle the boat by myself .
Its sounding to me like I should take the plunge and build the 12S, and use it for a while before deciding if I really really need it to be in two pieces. I guess it could be cut in half later and the two centre bulkheads added? Scary but possible? Maybe it wont even be necessary if I can figure the storage aspect out.
For interest, here's my little "home away from home", 32°19'5.02"S 18°19'49.21"E . You can probably see from streetview, why the dinghy needs to be easily carried - have to get it up those stairs - at least until I close in the downstairs . The bay to the north is perfect for sailing when the sea is flat, and theres a long estuary to the east - about 12km (8miles long). Very little sailing happens here, so I would have it all to myself! Once I get braver, some coastal trips should be possible too.
Thanks to all guys for your input, really appreciated.