The frequent mis-step has to do with shaping the stringers. The plans call for the stringers to be bevelled before they are installed, so that their top edge is level once they're installed inside the hull. This gives a straight, flat surface for cabin furniture to land on.
Its obvious once you've seen the hull right way up (or even upside down), but it's not obvious
when you are laying out the stringers.
Trevor built a jig for bevelling the stringers, to keep them all at the same angle. Here it is, partly loaded.
The decision we made was to scarf the stringers, instead of joining them with butt blocks. Trevor's background is in traditional boat-building. Scarf joints are commonplace to him, and he felt that it would give the hulls a cleaner look inside.
We tried a few different ways of cutting the scarf joints, but ended up going something quite simple: stacking the stringers, and planing the 12:1 angle for the scarf joints.
We glued them up on a long (40 foot) bench that runs down the side of our boat-shop. Each piece was assembled from three pieces -- two 16s and an 8.