First off a 45 Amps would probably be more than enough for the Caravel
. Just leave the switch/fuse box alone. Unless you want to update it as well. Then tear out and replace with modern auto fuses. You will need some kind of transfer switch. The wires should all be 12 volt
in the box. The 110 is in the rear by the Univolt. The Univolt is in the rear by the bath. That Univolt puts out 19 volts DC as well as 12 volts. The 19V ran the Exhaust fan and roof vent.
I think all the grounds (white wires) are tied together in that front area. So just pull a wire nut off the black and see what goes out.