The forest campground we have worked in also had the rule that the unit must be occupied during the first 24 hours and could not be left unattended for more than 24 hours after that. Reason was -- there were limited number of sites with electricity and they didn't want people hauling the campers in mid-week, taking all the electric sites for the weekend, which then prevented legitimate campers who wanted to camp mid week from having a site with electricity. It didn't matter that you paid - you were not there and the site was not occupied. Your trailer would be removed from the site.