> Hi, should bulkheads and deckbeams be installed before glassing the
> outside of the hull or the other way around.

I (a) installed the deckbeam and (b) installed, filleted and taped my bulkheads before glassing the outside of the hull. As another poster pointed out, while the bulkheads are on the inside, they help define the ultimate shape of the hull before you commit to 'glass.

With the bulkheads and deckbeam in place, the hull is much stiffer if you decide to turn and hold the boat on its edge while glassing the sides (i.e., to get a relatively flat, hopefully sag-resistant surface when filling in the weave of the glass on the sides).

Good luck