I think from the link you can only stay in official campsites - as for beaches..........er........if you can find one
Croatia's famed for its volcanic coastline, I guess from when it split away from Italy/rest of Mediterranean in year dot. If you can find some sand, your welcome to it.
Just reminded me of a strange story of my travels there - in the north you have Pula; we spotted this this guy with sea kayak, fairly hefty video camera and a well travelled disposition. Thought nothing off it.
Over the course of about a 12-15 days we travelled down the coast; Zadar, Split, the island of Hvar and eventually down to Dubrovnik and we saw the same guy several times, either off in the distance and once out to sea. By car that's over 700km. Would to have loved to stop him, talk and shake his hand......
........wonder if he blogged? <bimbles off to search>