Google isn't foolproof, but most of the time you'll be able to spot the attached decks, screenhouses, garden sheds and lawn gnomes....
The Woodall's guide also gives you a "% seasonal" reference also. Bear in mind that many private CGs cater to the seasonal renter....he's not living there, but has his trailer permanently parked "at the lake" and brings the family up there every weekend during the summer. Or if Mom is stay-at-home, she may be there with the kids for a month while Dad works and comes up on the weekends. Very few of those are living there full time because they are destitute.