: I'm struggling to match deck to hull, the deck has spread to give a max error
: of around 3/8" on both sides.

If I understand you correctly ... your deck is wider than your hull ... right?

I had a similar problem with my Outer Island although it was less severe. My deck was wider than my hull by about 1/8" to 3/16" on each side. My solution was to add spreaders inside the hull at each form location where there was a deviation. I stuck a piece of duct tape on the hull at each spreader location and below the seam tape edge. Next, I hot glued a small pine block to the center of the duct tape. Spreaders of the proper length were then inserted below the pine blocks. The spreader pushes against the hull and the pine blocks keep 'em from poping out. After you do the inner seam tape, just remove the spreaders and pull out the duct tape and wood blocks. A bent nail on a pole can be used to snag and pull off the stubborn ones. Be aware that this method will cut down the room you have to maneuver and glass the inner seam.

Ken