Waterproof housings for your cameras are your best bet. Depending on your rig, they can get mighty expensive though. However, they are worth the money for protecting your valuable camera gear. Audio wise you can do like we used to in the field and put an unlubricated prophylactic on your microphone. Yeah, it does get many a off-color comment, but the mic stays dry which is all that matters. If you prefer a more conventional method, if you have a recent sony consumer grade camcorder, one of these housings might work for you.
Sony Underwater Camera Housings w/built-in mic
