You can also beach camp in Florence if you actually want to camp out on the dunes. There are designated camping spots just for this at the South Jetty. Be aware some sites end up under water during the winter months due to heavy rain.
You also need to know about the Oregon ATV training courses which are required for ALL ATV riders as of Jan 1 2014. Getting the cards isn't difficult, but you do need to take care of it before you go. We've camped with several people that had to go into Florence at the Library to take the test and print out the certificates or they wouldn't be riding. There are exemptions, "Yes, all non-residents riding in Oregon are required to take the online ATV safety education course and carry an ATV Safety Education Card. They are exempt if they possess another state or country’s ATV Safety Education Card."
www.rideatvoregon.org