Balancing a flash with ambient light is fairly easy to do. for best results get the flash off camera..
I do recommend reading www.strobist.com which is a great site for information on using speed lights off camera.
I have just built a waterproof housing for my flash, which also mounts to my gopro line mount.
https://www.instagram.com/larsdanielterkelsen/?hl=enthis guy is the master at it... he has started using these
www.lumecube.com/ and mounting them in the kite and on the board