Great idea as so many people run their deep cycle or AGM batteries into the ground (i.e., flat) before they even realize it. Anything greater than 50% is bad on the batteries and negatively impacts battery life.
I would only offer a possible improvement that the LED be placed on the OEM status panel in the trailer.
2016 F281BIKS, Added Renogy DC-DC charger to better charge deep cycle batteries.
2003 F250 7.3L Powerstroke Crewcab longbed 20K lbs GCWR