Howdy. Not much of a surfer but I was pretty heavy into skimming & body surfing for quite a while. Still do both occasionally.
The gym is great, and will certainly compliment a lot of what you do. I suggest, however, that you not go the "sport-specific" route; i.e. don't attempt to mimic what you do on the board to what you do in the gym. The #1 thing that got me better at skimming & body surfing, was more skimming & body surfing.
That being said, a base program where you can pull away assistance as needed will work well. 531 would be a great choice for this. The base program with body weight assistance is what I'd do were I in your shoes. You'll keep getting stronger with the base program, and gain a better control over your body with the body weight work. No need to get too fancy either. Keep to the staples like push-ups, leg raises, chin-ups, lunges, etc.
Good luck in the competition!
EDIT: Also make sure you're doing jumps Agile 8