most were installed during a period when it was really hot, and really rainy. Now it has cooled off and the humidity has dropped. It's nice to be outside, but the strips running along the length of the boat have contracted, and opened up huge ugly gaps. I assume I'll have to cut most of them out and try again, but I want to know how to prevent this from happening again. If I fair/sand the boat and put a coat of resin on it, will that stop or at least restrict the movement? Any help will be greatly appreciated.

Wood expands and contracts with ambient moisture changes. Most across the grain but with length also. This is why I use an external strongback which allows the ends of stems to be tied to the strongback and supported. Unsupported stems can be pulled out of alignment by full length strips moving with changing moisture conditions. That's why it's best to apply equal numbers of strips to each side of the hull before stopping for the day.

Working outdoors will subject the wood strips to greater moisture fluctuations. Usually there will be less problems in a shop, but if stripping takes place over a long time period the chances for expansion - contraction problems increase.

Coating one surface with epoxy will "freeze" wood movement on that surface but the other un-coated side will continue to be effected by changing moisture in the air.

I have experienced problems on the hulls stripped in the winter, where my shop becomes drier and drier. With the exterior sealed the interior continues to shrink and curl inward.

By understanding the problem, moisture loss, I can correct it by adding moisture, wetting the interior until it expands to the correct dimensions. And with a surface too wet, I would dry it with a heat gun.

I keep a moisture gauge in my shop to tell me when I have big swings in humidity.

I hope this helps you understand the very sensitive interaction of wood and moisture.

It can come as a surprise. Plastic doesn't do this!

Good Luck

Rob