I mounted my Progressive Industries hard wired unit behind the removable panel on the right side of the storage compartment. I found I had plenty of extra cable from the back main plug to the distribution panel so rather than mounting near the panel and adding additional wire I cut the main wire.
I mounted a piece of plywood to the aluminum framing and mounted the unit on this. My model is more difficult to mount than the one you have purchased as everything has to fit in the box provided, a little more difficult with these heavy wires.
I did not want to make additional holes in the panel for mounting the remote monitor so I took the thermostat off and ran the wire up the same hole used by the thermostat. This allowed a mount with only the two small screw holes and is in a perfect spot to observe what is going on.
Total time for my install was about 3 hrs, make sure all your connections are "tight". Good luck with your install.