Sometimes you need power for a supplemental brake system too, e.g. a Brake Buddy. Or to power a remote indicater in the motorhome that tells you when/if the toad brakes are being applied.
But basically, you are right. A battery disconnect does the job. However, dead batteries are not a common problem in older toads - it is mostly the newest models with a lot of electronics that are powered whenever the key is on.
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL