Alena,
As for the 2 holes above the Serenity *windsurfing* logo on *top* of the stern's deck, there are indeed 2 holes (at 55 cm and at 65.5 cm from the stern of my Serenity mk I wood) with plugs to let you screw in 2 screws and washers to attach the Starboard rolling trolley called the "Clipper Wheels" (
http://2007.star-board.com/viewpage.php?page_id=11). These 2 holes are perfectly normal and watertight, no worries.
Cheers !
JM