We also ordered sea safe at drugstore.com. Funny we ordered it on a thursday morning and took the free shipping option (since we had plenty of time till we needed it) and it was there the next day.
We used the sun screen at castaway cay, but not when we were on the beach at St thomas. We didn't have problems either time, so not sure it is actually necessary, but i guess can't hurt either. You need sun screen anyway.
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