I sanded the tip edges until they were all the same depth on the little indented part. This gives a consistent fit all around the tip as it slides into the aluminum wing. Then I trimmed some of the aft end off to clear the ailerons. Wasn't sure what to do here, so I just trimmed to fit. Drawing says 1/4 inch gap. I made my 3/16. 1/4 seems like too much.
