Keep in mind that this is not all of Montana, just Billings. A better way of fighting this is 2 fold.
One let the town of Billings know you will not stop and will not spend money there. Make sure you pass the information on and definately bypass the KOA campground which is owned by the main protagonists for this law.
Second ask at any campground is they are a member of the National Association of RV Parks and Campgrounds. This organization is promoting legislation like the Billings ordinance and offer packages to "help" campground owners lobby for laws to require all camping to be done in a "licensed campground" to protect their business. In short they want to promote a law mandating that their business be used or face legal consequences. If they are a member of that organization pass on staying there and let them know why.
Of course I am assuming you will boycott KOA and also let them know why. If you go to the ARVC web site (
www.arvc.org) you will see KOA is VERY prominant.