Dh & I have expensive bikes that we 'do' keep in the back of our towed suv. We do this for the Smokies as that's mostly where we take them - don't bring them to the Fort.
I know this would not be feasible for a family of bikers. It's really sad that we can't trust all our fellow campers - thankfully most are good solid people.
Actually, I've seen some really lax people with their belongings at camp sites - toys, bikes strewn all over the site when they leave. Guess some of these thefts of locked bikes (not all) are in protective sites. Impossible for CM's or neighbors to see everything going on.
I would advise bringing older bikes or renting them. Thieves are most likely looking for resale.
I worry about my Mickey Lamp - a special gift that our ds made me for my birthday recently. I wonder if any of those get stolen?
Am thinking about getting an alarm similar to a simple window/door alarm.