I am very open to suggestions for tagging this better.

I take "fee" to indicate whether a motorhome can stay overnight for free.

But you might have to pay for electricity, water, wastewater disposal, etc.

I try to tag this when I know it. But sometimes I just have e.g., a tourism website that says that you have to pay for services without specifying which services there are at the site and which of them you have to pay for. Sometimes you have to pay for all of them. Sometimes you have to pay for electricity, sometimes for both electricity and water. So I tag it with service:fee=yes.

Hopefully someone visiting a caravan_site will replace it with more specific tags.