Check out www.campendium.com which gives you the option of picking free places from the map
also check out boondockers welcome, which used to be free but is now $50 for a year so have a look at it before joining, this is people who have spaces you can stay in for usually one night and may be at their home etc.
We tried Harvest Hosts as per Boat Addict, but at the time out West there were very few locations to stay so I suggest checking out their map to ensure you have a good choice of where you are travelling before the expense of joining.
Hope you find something decent.