What is it your husband is trying to protect against?
We used to lock ours, but haven't for the last 10 years. Just not something we worry about, but I guess it depends on where you go. But if I had tow worry about somebody stealing my car off the tow bar, or stealing the tow bar itself, I probably wouldn't go there. We don't tow through city areas or park where vandalism is common either. Others may not have that choice.
The fire disconnect thing is a valid concern, but chances are you won't be able to get the toad off anyway. RV fires often start at the back (rear engines or rear axles) but wherever they start, they spread fast and are probably too hot to approach by the time you get the people & pets out. If the car is hooked up, it's probably a goner. Or not worth the risk of trying to work up close to a burning coach.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL