I installed the bulkheads on my two builds after the deck & hull were joined and the hatch openings were cut out and it was a real PITA. I know some here install the bulkheads into the hull before joining to the deck (I believe ET has mentioned it is his method) and that is what I will do if I build another.

I imagine the trick in doing it before joining the deck & hull is to make sure the top of the bulkhead is properly sized so it doesn't interfere with joining the two sections but that shouldn't be too difficult to achieve as long as you are careful.

:D