I split the wiring to go down one side of the heater box or the other, depending on where the wires needed to end up in the wings/tail/cabin. Some split conduit covers the wires from behind the panel to under the center tunnel. A couple of zip ties holds the conduit in place. I had to open up the left side where the brake lines on the 9A model enter the center tunnel. The other side is already opened up for the wiring conduit.
Left side:
Right side:
I made the heater control cable on the right side enter aft of the vertical angle so it clears the conduit, rather than penetrating the angle like in the plans.