According to https://wiki.openstreetmap.org/wiki/Tag:tourism%3Dcamp_site

capacity:caravans is the number of pitches for both caravans and motorhomes.

these 4 sites are 
tourism=caravan_site, caravans=0

So there are no room for caravans (trailers pulled by a car).

But we cannot use capacity:caravans=0 because then data consumers (e.g., opencampingmap)  will interpret this as there is also no capacity for motorhomes.

So a site like https://www.openstreetmap.org/node/11038816129

has room for 10 motorhomes and 3 caravans.

The only way I can see to confer that information is capacity:caravans=13,capacity:motorhomes=10.
Maybe we could add e.g., capacity:trailer_caravans=3 

It is all a bit of a mess because the name "caravan" is used in a very ambiguous and confusing way in tagging. 