Sit on tops are fun (we used them on vacation in the Keys and BVI), but they are definitely for bathing suit paddling and warm water only -- you are basically sitting in water the entire time. Not a lot of water, but they aren't like kayaks that you actually sit inside on a seat and have some reasonable hope of staying dry.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow