Mike...good advice...One more thing you might add to your list of things to be careful about when using a notched spreader.
Make sure all batches of thickened epoxy have the exact same ratio of cabosil/glass bubbles/epoxy from batch to batch...if it changes...you will endup with soft batches and hard batches...the softer mix will sand easier and the harder batch will not. This can create some real issues when trying to get a fair hull.