Finally got around to this mod today. I bought a battery shut off switch here:
http://performanceplusconnection.us/...B0017101BE.htm. - a little pricey, but made to do what I envisioned.
The battery is stored under the leg of the "L" of the couch. I drilled a 3/4" hole where I wanted the switch - just to the left of the 110V outlet and above the heater duct outlet, where the couch juts out. The switch mounted cleanly, looks professional, and works well. I like the fact that it's inside the trailer, but in an easy to access and out of the way place.
Works great!