If you enjoy working out side, I would recommend giving De Rivera Park (the park down town) and B dock a call. Ask for Tom. There is limited housing, but a Marine would be right up Tom's alley, he would probably hire you on the spot with out an interview!
Not to mention I've had just about every type of job you could have on the island and working there was by far the most fun job I've ever had. Taking care of the park is very rewarding, but the best is being a dock master on B dock, it gets the most regular boaters and you can meet lots and lots of great people who come almost every weekend. I'm still friends with many of my old regular boaters. There are great tips to be made, not uncommon to get a $50 to 100 dollar tip from one boat, plus other types of tips, food, go to the bar when there are a bunch of boaters there and you rarely have to buy a drink, they'll bring you all kinds of gifts. You'll have a great tan...but really the best of all is the friends you'll meet down there, the boaters really are great people.
But whatever you would choose to do on the island you'll have fun, the employers all do lots of nice things for the employees and all the summer help is so nice. You can't go wrong working on the island for the summer.