I swapped out a Magnetek for a Progressive Dynamics converter years ago.? If I recall correctly, I just combined the two (+) wires at the converter (+) output.
According to the Winnebago wiring diagram, the two (+) wires are blue and red. One is 'regulated' and one is 'unregulate' (also IIRC).? The blue wire goes the interior lights, refrigerator, furnace, and LP detector.? The red wire provides 12V for everything else on the camper side (water pump, monitor panel, and so on).?
The white wire to the converter is ground.