Checking across the terminals is meaningless- it doesn't tell you anything. You need to check between the terminals and ground.
We know the panel is getting power because the refrigerator, slides, jacks, etc. are working, and they are the other leads hooked to other breakers.
I'm not really sure what a fuse checker is, so I cannot comment on that, but it sounds like a test light, which would mean the problem is in the kill switch.
To find the kill switch, you will have to trace the wire from that panel- it will be in that wire, somewhere between the panel and the inside fuse panel- but probably in that front compartment. This *could* be an option, but the schematic shows it, and not as an option.
