Brian, why don't you use the Miami-Key Largo Race? That is exactly the distance you are looking for, all on protected water, and the event already exists -- except it's in April.

With the Miami-Key Largo, the Hog's Breath 100 and the Mug Race all being on consecutive weekends, that's already a lot of distance races that time of the year. Not to mention the Tybee 500 coming right after them.