My wife and I have toured close to a total of 18 months in the last 10 years and have not had anything stolen, except by raccoons, ravens and chipmunks.

Rural areas are not usually a problem. However, a good cable and a stout padlock, weighing less than half of your chain and U-lock, will provide security from an opportunistic thief. We've also used the cable/padlock combination in larger cities, but were really selective about where we parked our bikes. There is usually something to lock your bike to: picnic table, tree, or pole. If all else fails, lock all your bikes together in a big "wad". it take several people to move 2-3 bikes locked together, and it will not be done quietly.