In reply to Tobes:
Hopefully someone with more specific experience will be along soon, but just a few comments based on a 7-week rock climbing road trip by campervan last autumn...
I love Croatia, and visiting out of season is magical. The tourist infrastructure is great at that time of year - most things you might need are easy to obtain, but no crowds or high-rise development.
Re drinking water... I have to admit to still being a bit cautious, but it's perhaps irrationally based on a GI infection picked up there nearly 20 years ago. But in remote areas it might be worth using a filter or purification tabs. Sorry, I don't know about gas, as we didn't need to re-fill.
I assume you know that wild camping is illegal, and is sometimes enforced, but if you're staying in huts that shouldn't be an issue.
Hopefully you won't need it any emergency help, but if you do, we had to make a 112 call in a remote area (on someone else's behalf) and the call handler was brilliant - she spoke excellent English and the police arrived promptly. We've also used the doctor's surgery in Starigrad Paklenica which was very good.
For your beach days, the beaches are mostly rocky but very beautiful. And we've had wonderful sea food in the coastal restaurants.
Hope this is of some use - I didn't reply earlier as it didn't seem entirely relevant, but in the absence of any other replies...