My take is that that boat was designed to be built either as a one-piece or as nesting. I'd pick one and stick with it.

Laszlo

Sounds like the measures you'd take to get rid of the cardboard and then prevent moisture from getting trapped in the gap would be only a bit less trouble than going ahead with separating the parts.  If you don't saw her in twain now, my guess is you never will.  Having already paid the penalty of having the weight of the extra bulkhead, you may as well gain back the advantage of being able to separate the boat whenever you want...without needing a saw.

Remember, just because you can separate the boat doesn't mean you must always do so when she's not in use.  If you spray some silicone over the mating surface of the rubber gasket (the other surface should be affixed with rubber cement) so that the parts will separate cleanly, you can leave the parts attached for an extended period of time if you don't need to store the boat between outings.

Our PMD take-apart will often spend several weeks in the assembled state, sometimes upside down.  The whole business is quite strong, so I wouldn't worry about "breaking" the boat by storing her upside down or some such when assembled.  My adult son and I have sat on the upturned, assembled boat without harm.  We did add large SS flat washers under the star nuts to spread the load a bit when tightening up so there'd be no chance of making "divots" in the bulkheads by over-tightening.

Besides, if you don't finish the job, you'll never get done answering bystanders' questions like, "What's this here extra piece for?"  Instead, even landlubbers will see the thing and exclain, "Oh, how cool!  Your boat can be taken apart!"

The sawing in twain event is a good time to have friends and family around to help, both physically and emotionally, so pick a day, arrange for pizza afterwards, buck up your courage, and take up the saw!  I'd save any adult beverages for afterward, though you might want to prescribe 30 cc Rum PO PRN for the sawyer, by way of steading his nerves, being careful not to make him unsteady by overdosing him.  <;-)

.....Michael