I purchased the Magnum MS2812 inverter and the installation material does not provide a definite place to ground. What do you recommend?
The inverter chassis ground needs to be one size smaller than the largest wire connected to the inverter. With a Magnum MS2812, your wire size should be 4/0 for main DC positive and negative, as such the chassis ground should be 3/0. In terms of connection point, the chassis ground should be brought back to the large ground distribution. This ground distribution should be connected to your DC negative, AC ground, bonding system, etc... Make sure that is at least a 3/0 path all the way to the battery.