The battery was usually on the outside front under the window. It was a more narrow battery than what is used today. The 110v and 12v
systems are completely separate on 1961
Airstreams. There was no converter. Each light fixture had two separate lights in it, one 110v and one 12v
. There was no 12v
fuse box. Some trailers had a couple of 12v fuses in the front of the trailer behind a cover in the wall close to the floor. The 3 fans, furnace, stove vent, and roof vent, had transformers so they could be used on either 12v or 110v. I use to own a 1961
Overlander. You can search Airforums to see how others have converted their vintage Airstreams using a modern converter and 12v fuse boxes.