We take a general European road atlas, such as the AA European Road Atlas http://shop.theaa.com/store/shop/aa-...as-europe-2014
and find that that, together with the sat nav, is good for route planning. I'm also like to keep a record of where we've been so also take a road map http://dash4it.co.uk/croatia-sloveni...phia-6474.html
to record this on.
So far as destinations - what are you looking for? The coastline is spectacular but we love the islands, Krk and Hvar being our favourites.
Istria, a peninsular in the north of the country, is a good place to start, having plenty of campsites right on the sea plus there are some pretty towns like Porec, Pula, Vrsar and Rovinj.
Further down the coast the Zadar region is less touristy on the coast but has the advantage of 4 regional parks inland, Kornati, Plitvice, Krka and Paklenica, all worth a visit but if I only had to choose one it would be Plitvice - a series of lakes and waterfalls on stunning scenery.
After that you come to Split, a lovely old city with the Diocletian Palace at it's heart, plus this is the jumping off point for some of the most beautiful islands - Hvar, Brac and Viz.
Carrying on down the coast you come to the Dubrovnik. Incredibly touristy but a beautiful city well worth a visit, as is it's islands. You do have to pass through a 'corridor' of Bosnia to drive to it but it's no problem.
Wherever you go don't expect sandy beaches. Most are pebble of rock, or even concrete in some places!
If you do go to Slovenia then most people think that the must sees are Bled and Postijana and they are worth a visit as is he city of Ljubljana which has a convenient campsite on the outskirts. Portorož, on the coast is also a pretty town famous for it's roses, as it's name suggests.
There are plenty of campsites in both places, some of which take ACSI but check on the seasons as they differ from, say, France. Wild camping is not allowed in either country.
This is all very general but if you can let me know what sort of thing interests you then I could probably be more specific. We know the country very well so if you want any info please do get in touch.