I went to the rig for a look.
The GoPower label fixed to your back wall is the cut out template for the controller that you NEED for the solar panels (if your using the ultra over priced GoPower kit) Read the bottom yellow sentence on the label.
The 8ga wires are hanging behind the wall. *Second picture*
The 8ga white (negative) goes to the converter negative ground, I'm assuming (I don't feel like following it)
The 8ga red (positive) goes to the battery power area and is attached to the breaker. *center of bottom picture*
I don't know how long the wire coming from the roof is but I assume 20', it should handle at least 20-30 amps. Someone on here that is solar savy can verify.