Campgrounds or caravan parks in USA like Australia and New Zealand would mostly require minimum days of stay. Some 3days, others require a week. Say you do not have the luxury of time to observe this, and you wanted a roaming RV vacation and rented a USA RV that has everything (toilet, shower, hot & cold water) that should earn convenience while doing a “free camping”. Without these facilities, you should consider where to park or stay for the night, some place that can provide access to basic facilities.

In USA “free camping” is a lot like “boondocking” with definitions pertaining as free camping itself, overnight RV parking at truck stops, and places that do not have RV hookup facilities are referred to as boondocking. Boondocking is posssible in USA but it doesn't mean everywhere...or campgrounds would be useless. Boondocking is allowed anywhere on federal public lands within 300 feet of any established road, except where otherwise restricted. US National Parks DO NOT allow overnight parking and boondocking. There are limited private campgrounds that allow overnight parking. Farms, ranches and other private lands could allow you for a fee you can't complain.