I'm currently vacationing on Marco Island in a rental home.. (Trailer is in storage)
There are 2 campgrounds out on SR 951 on the approach to the island.
1 is a KOA that just yesterday I rode thru to see if there were any Fiberglass
trailers in there - it's packed but there were spaces available (about 4) when I went thru. Nice pool, looked to be activities quite a few seasonals there. There's another across the street, but the name escapes me right now. It's more shaded but looks packed. I haven't driven in there as of yet to go 'Egg Hunting'.
Then there's the State Park south of 41/951 - little more remote and primative with no pool or anything.
These are the only places I know of. Naples is usually known for it's multi-million dollar homes and good shopping!!
Good luck in your search! High this week is supposed to be 75 - it's been quite comfortable and sure beats the 18 degrees and snow back home in Ohio!!