Gary,

Two winters ago I built a Tern in the living room of my apartment, and I had some panels warp on me. I think it was due to moisture from showering, boiling water in the kitchen, etc. I had no problems stitching the boat together. I had one panel curve a bit upward at the end, and stitching forced it into the correct position. I had another panel, though, that warped the other way -- kind of like the way a blade of grass forms a slight trough-shape rather than flat. It was one of the lower hull panels. If you lay a ruler across it, the center is about 1/8" away from the ruler. The other hull panel is flat enough that the ruler touches all the way across. It annoyed me at the time of building, but hasn't affected the handling or look of the boat.

Dean