Use Norfolk Lines, (usually cheap) then go through Valkenberg Rudesheim, Nuremburg, (Nice campsites at all these places) Pass Munich And another campsite at Traunstein and then to Lake Bled.
We have gone this way, more or less, twice as there is free motorway most of the way if your time is limited. Beware of the motorway tolls in Austria if you are driving a big motor home. Small ones are not expensive. Bit slow getting through the Slovenian border but no problems. If you go down to Dubrovnik you have to travel through about 10 miles of Bosnia. They try to sell you insurance but it is a good straight road and nobody bothers!
Hope this helps! Enjoy