In the third photo, there are 2 hex nuts on the back of the fuse block.
Connect the negative wire from the PD 9245 to the nut on the left. Connect the positive wire of the PD 9245 to the nut on the bottom. Notice the the bottom nut is on the screw that is in the center of the copper buss bar. This is the positive side of the 12 volt
You need to be careful where you mount the fuse panel. You do NOT want the positive terminal to come in contact with the skin or frame of the trailer.