I had to remove the toilet and the bathroom floor board to allow easy access to the space beneath for wiring. Surprisingly, the removal process was very simple and took all of 10-15 minutes.

This is the space with the toilet and floor removed. I covered the blackwater tank drain with a plastic bag to avoid dropping anything into the tank.

This is my finished wiring job. The main 4 ⁄ 0 positive and negative cables go through the wall on the left to the inverter. A red cutoff switch on the left is installed so I can easily reach it once the floor is put back into place. This will isolate the battery from the inverter and charger. Also seen toward the back of this space is the 1/2 inch split wire loom that contains two 110v cables and a 4-wire telephone cable originally used for the battery temperature sensor and later used for the battery shunt current monitor.

The cylindrical object is a housing that protects the 300 Amp T-fuse. I made this up so I could easily loosen the clamp and slide the housing off the T-fuse in case I needed to change the fuse for some reason without having to take the toilet out again. This is made up of a rubber plumbing 1 1⁄4 inch PVC pipe connector with an adapter on each end that restricts the opening enough so the fuse assembly can't slide out. You can better see the red battery cutoff switch on the left (Blue Sea Systems m-series battery on/off switch rated at 300 amps). I had to slightly enlarge the openings on the switch so the big 4 ⁄ 0 cables would fit into it.

This is where the positive and negative cables pass through the van floor. I used a 1 inch cable strain relief through each hole to hold the wires firmly in place and to protect them as they passed through the floor. You can also see the flexible split wire loom covering each of the battery cables. The 8 AWG green ground wire is seen with a crimped lug and screw grounding it to the van metal floor. The telephone type cable is the excess wire lead for the battery temperature sensor, which then runs with the negative battery cable to the rear battery compartment (I no longer use the temperature sensor, but instead use this cable for the battery shunt monitor .

Finished project with bathroom floor compartment door closed

Bathroom floor compartment door opened, revealing the shutoff switch for the positive battery cable going to the inverter. This can easily be reached to turn off the battery for storage. You can also see the telephone type cable just above the switch which I ran along the front left corner of the bathroom wall up to the battery charge displays. I secured this cable using white silicon caulk so you can barely see it even if you look for it.