Another option is to use google, but target the search only to craigslist.
example, if I was looking for "school bus" I would type the following into the google search bar:
school bus site:craigslist.org
that will return results containing the keyword "school bus" from all cl sites nationwide.
The same is true with any site, I use it all the time to search skoolie.net and it works great, just today i used it to search for info on the Cummins NHH 220 and got exactly what I was looking for.
Cummins NHH 220 pancake site:skoolie.net