I test fit mine all over last weekend. There wasn't anywhere that would work that was in reach of the batteries without extending the 24v/12v source wires.
Behind the passenger seat interfered with the seat back, same as in the well for the slave plug.
Mounting vertical under the passenger seat would put a fair amount of stress on the cables due to the angle they would be bent.
Mounting under the dash would work but looked messy.
Mounting horizontal under the passenger seat seems to be the best "in cab" place to mount, but I am rethinking it as there could be an issue if I wanted to put in a radio or other comms under the seat. Plus its not the most convenient location and would require more holes in the body panels to mount.
I'm considering mounting to the frame rail under the bed as there is a good amount of room. Possibly even above the fuel tank.
Open to suggestions if anyone else has a better idea. I am planning on completing the install this weekend between rain storms. I will take pictures during the process.
ETA: Also could use some ideas on mounting the solar panel or creating a removable mount for it.