Jay said:

I never have installed it during building when the hull is open and available. Maye that's a good idea? I just never have done it then.

I'm installing the bulkheads into the hull prior to attaching the deck

I've never installed bulkheads before joining the hull and deck, because:
I don't use sheer clamps unless I absolutely need to, and I can't do a decent job of taping the inside seam if there are bulkheads in the way. A good seam tape job is stronger than a small cross-section, long grain, sheer clamp, too. For a boat with a sharp 'corner' at the hull-deck join, a sheer clamp is a better idea, since it's very tough to get seam tape into a corner.

Fitting the bulkhead is easier if the hull and deck are joined.

It's much easier to do a clean job on the coaming (if laminating a glass or carbon coaming in place) without the rear bulkhead in place. Even wrapping glass around a wood stacked coaming would be more awkward with the bulkhead in place. The closer the bulkhead to the cockpit, the more this becomes an issue.

Also, it's just easier to figure out where the bulkhead needs to be with the deck permanently attached, though I suppose I could do it with the hull and deck taped together.

But lots of builders put the bulkheads in before joining hull and deck, so I guess a different sequence and system will work.

BTW, for folks who haven't installed bulkheads before, it is MUCH easier to do that work with the boat inverted and your butt on a nice pad on the floor. Same for installing thigh pads.