Working in the vertical plane may not be the most usual way of doing it, but scarf clamping and lofting can be achieved this way with a little determination. If I can’t get outside, then bulkheads will need to be cut in the vertical plane as well.

I decided to go with Slight variation of thickness (c 0.5-1mm thickness variation in the finished panel….won’t do that again!! Also, clamping with thicker stock (2”), didn’t allow for enough pressure in the thinner area, so I’ll have to fill with epoxy/wood-flour mix, or start again. I went for the fill option, using this portion for the very gently curved stern end of the panel.

Scarfing ended up being better with thinner stock and plenty of drywall screws to clamp the joints, with the clamp being just less than the scarf width in each case...