Where did you get your information that the thimbles peak in june? My understanding was that they had the potential to be around all summer, but that they peaked in april and may. Also, if you are interested in the Caribbean, anywhere you go could have them at that time including the Florida Keys, Coz, and Bahamas. I was very worried about them too, but I just got back from Roatan 2 weeks ago, and I only saw them on one dive, had no stings, and had no signs of SBE from their larvae. Its one of those things that people talk about as a "watch out for this", but its really not a big deal, and at least to me would not be worth skipping the great diving in the Caymans on the off chance you might get a sting or two.
Aggiediver