Did hvar and brac as a fly holiday so cant comment on campsites. Lovely islands.
Krk Vir and Pag did with motorhome, all great, was a little disappointed in Vir and Pag, not sure why, just expected a little more.
In my opinion the islands don't offer a great deal more than the mainland.
I think I'll mostly stick to the national parks and mainland now I've seen the islands.
Probably go back to Krk at some point though as I did love it there and it's easy to get to with a road bridge.
Most campsites in Croatia are of a very high standard but some are vast, 800-900 pitches ! I avoid those.
Look for the small campsites of which there are many.
'Camp Romantik' just outside Labin (Istria) on - route for the Cres Ferry from- Brestova is highly recommended - only eight spaces out of season but with all the facilities you could ask for; usual sanitary facilities, small heated pool, BBQ, kitchen facilities and appliances for your use.
Done most of the islands and agree with above. The islands are the same as the mainland. Both have beautiful coastal towns. We did the entire coast of Croatia last year and always prefer the Makarska Riviera. One of the best places we found was Zaostrog , it has an ACSI site there.