Thanks, Sean. I had been going by the seat of my pants on how much gelcoat to use. I was told a good rule of thumb was to use a mold material with a contrasting color and then use enough gelcoat to hide it. Turns out that wasn't enough. I consulted a professional and was told 12 to 15 mils of gelcoat minimum. So I've been calculating the correct amount for each part and laying it on as evenly as possible except a little heavier at corners and edges. That seems to be doing the trick. The outer boxes and the parts I did this week have no alligatoring except a few tiny wrinkles around the margins, most of which trimmed off.
Dave