How do I create an ad-hoc network when I change to a particular Network Location?

The scenario: In Car Mac mini
After changing it to the 'OnRoad' location after using the 'Garage' location (that's configured to connect to the home network) I'd like it to go into adhoc mode to network with other similarly configured cars and laptops. Rather that having to type in each time the same network name and password automatic creation would be a blessing. It'd also reduce the hassle and chance of typos.

Thanks for any help you can give.