We stayed one night at Karlsborg camping on our way to the west coast. We got a nice flat spot to put our caravan on. The service buildings were clean during our visit, but they are a little small and crowded.
The camping has direct access to a smaller lake with nice child-friendly bath, no need to dip your toes in the much colder lake Vättern. Not far away, easily reached by bike, is the Karslborg Fortress with its interesting surroundings.