Just brainstorming..
It might be good to keep the attachment system on the inside of the hull, so the exterior is smooth enough. Lets say for example that you just bolt together the two bulkheads of both halves. You could plan the storage part in the same area, so you have access to work on the inside. You could isolate that area of the rest of the hull with another bulkhead, so any possible leak is limited to that volume.
Now bolting the two bulkheads might not be the best idea, because bolts are doing a lot of work. What about creating a male/female piece on both bulkheads so you you can bolt on a surface perpendicular to the bulkheads, where the bolts would make a lateral force. It would also add strength to the structure.