There are all kinds of places you can park for free like WalMart, Most Indian casinos offer free overnight parking. WalMart sells a road atlas for under $10.00 that lists the address of all their stores.
Camping World sells a book on free overnight casino camping.
http://www.campingworld.com/shopping/item/casino-camping-6th-edition/70670I would stay out of large towns and off the main highway that goes through the town. Our town is so small it doesn't even have a police department. Another place to look for are trail heads which are usually within a couple of miles off the road. they normally have parking places for hikers to park their cars and are seldom visited by the authorities.