Nice work. When we had our North Trail I added a battery shut off as well but ended up mounting it out of sight on the front beam where the outside light is mounted. Someone decided to play with ours once and if I had not caught it we could have lost a fridge of food.
I added a battery disconnect as well on our M32. I chose a larger battery box http://a.co/1iD5i46 and mounted this version http://a.co/dn0mWRn inside with contact grease. Keeps it nicely out of the elements and I no longer need to used the tie rope around the battery box. Both clips hold the cover firmly in place.