Just a curiosity on my part. Wasn't sure from the initial post if he was using a resin with a long enough working time. Z-Poxy always worked well for me. Extremely long working time, lays out well and sands like butter. If he's using a polyester and isn't mixing it exactly right, he could be running out of time as it begins to kick helping to cause the waves. I would bet it's a combination of not enough saturation into the wood and glass combined with getting towards the end of the workability window. Ask me how I learned that lesson.

Dan