Woodman, I consider a bulkhead as necessary, and in the way. You can reinforce the underside of your decking very simply by glueing on a 3" - 4" wide strip across most of the deck width. On a deck that is peaked, and not rounded, I've glued a strip across by just glueing its ends to the underside of the deck. This leaves a gap in the middle, where you could add a short vertical piece.
These simple braces will add stiffening to a deck without adding a lot of weight.
Here is how the mock-up is looking. The 2 bulkheads are 5 feet apart and the front one I will cut an access hole in.
The flat part of the rear bulkhead is 15'' wide tapering back to 10'' wide at the transom.