I've been stuck at 9 for weeks now =/
Annoying thing is I've had several at the campsite, but the only one I wanted to move in - wouldn't!You'll need to visit another town who has one moving out, or go to the campsite hm :/
Just as I thought there was finally a confirmed answer!
The confirmed answer is 10 villagers + someone in the campsite.
However, if you are at 10 villagers you cannot try to get the animal in the campsite to move in.
If you have 9 or less villagers and someone is in the campsite you can try to get the camper to move in.