Peanut went into boxes today, and in my campsite is Marina. I've kept on trying to talk Marina into moving in but there was no mention of it. Is there any way she can? ;--;
A camper is still possible even with a full town. That's what the op also mentioned. Since you already have 10, even if the last one is about to move, there would be no mention of them wanting to move in. They can still play games and have a conversation with you, but no dialogue about the town being amazing and them asking to be apart of the town.
It's sad since usually it take about 2 days to a week, which is enough time for the 10th to move out, before the camper can move in, but alas that's not how the game works.