We do have an ACSI card but did not use it very often in Croatia. It is not expensive, so we reckon it is worth carrying.
We found a few sites in Croatia that were cheaper for three days plus than the ACSI rate. If you only want to stop a night or two at each site, it’s worth having it. You can look on the ACSI website, I think, and see how many campsites have a special rate for it. We did wild a few times but very much out of season. But I have heard of people being fined a significant amount recently. There are also a few aires.
We also used the usual apps for finding spots and reviews of sites. Some sites were shut when their web sites said they were open, so have a plan B.
Sites need to be booked in high season right through to October as Croatia is so popular. Croatia is very popular with the Germans. But particularly around Istria where we saw miles upon miles of stored Caravans and at least half of them had German plates. Also in season there were a lot of nudist campsites … Should you be interested!
Take a look at our sleep spots page.
When you have paid for the ACEI card you can download their app. This as well, as the book, will give the dates and the prices for each of the campsites. The app allows you to filter dates. Dates do vary by site.