My family is considering traveling to Costa Rica this summer. 2 kids, 15 & 18. Where is a good area to stay with a beach. any hotel suggestions? any other suggestions?? Also are there lots of jellyfish in costa rica in the summer?

I am going to costa rica on a mission trip, and i was asked to take pictures for the trip. I want to bring my D90, but I know the moisture and humidity is REALLY bad there. Like, 100% humidity. So, i was wondering what I could do to keep my camera protected.