Not sure we are talking the same fuses. I find the 12.3 volts in a fuse box in the engine compartment on the fire wall. Book shows there are 12 fuses there. Book also shows a fuse box by the break peddle, can't find that one but found a fuse box in the side of the bed, not mentioned in the book. This fuse box has 13.6 volts in it. I believe the box by the bed is the box that should be by the break peddle. These fuses distribute DC around the camper...lights, fans, etc, the one on the fire wall seems to be for automotive stuff....turn signals, break lights, etc.
The question; does house battery voltage reach fuse box by bed if all else is disconnected is still valid and will be checked out.