I can't tell you much about sites in northern Slovenia but we caravanned for a couple of weeks at Camping Galeb at Omis, south of Split, in August 2010. In our pre-planning we found the "Alan Rogers Italy, Croatia and Slovenia" campsite guide very helpful.
We visited Camp Bled in Slovenia on the outward journey as well as stopping off at 2 German campsites each way.
Generally camp sites in Croatia tend to be VERY large. Beaches are, also, in rather short supply. Camp Galeb had one but I wonder if it was not partly man-made.
You can read my review in campsite search section
Croatia is a lovely country with friendly people and still relatively low prices. If you're planning on driving it seemed a long way to us. Our round trip from St Helens, Merseyside to Omis via Dunkerque was 3,300+ miles.
Camp Amarin, in Rovinj, about 10 miles I think from Pula, lovely site, staff all spoke English, right by the sea, with pool and slide, boat trips, have done a review. Any questions, don't hesitate to message me.
------------- Julie
Summer 2016 Camping las Dunas, Spain
Woop Woop I won £50 of Halfords vouchers for one of my camp site reviews - make sure you do yours!
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.
Topic: Camping Northern Croatia
