Sue as said above, if worried get a stinger suit, they're cheap insurance.
Lungs is the first windsurfer I've heard of who's been stung and bugger that

One of my kitesurfing mates also got stung one year (foot) in FNQ but he was doing it in light northerly wind, big no no. Generally box jellies don't like rough water, the old idea if windy enough to windsurf they wouldn't be around but who's taking the chance. I've sailed about 20 stinger seasons using a stinger suit, spend too much time in the water and have been ok
I've sailed Burrum a few time and always just boardies. PM Hooray or one of the other locals for info, or KA72 Kellie if no locals see your post ?
Lungs I used to wear my boardies over, it's a toss up which looks worse, that or an old bugger in a lycra suit