If we are staying at the campground in our RV for the weekend, do our friends have to pay to visit us during the day on Saturday?
I think they would need to pay to park their car in the campground for the day.
Probably a small day use fee. Call them, great staff.
Have them pull into the free day park picnic area which is adjacent to the campground. There generally hasn't been anyone at the entrance but parking an extra vehicle in the peak season might be a problem for some of the spots.
Get quick answers from Collier Memorial State Park staff and past visitors.