If you use an Opus DC-DC power supply, it has built in shutdown functions, or you can buy a shutdown controller. Opus might not support a really high power system though, although I hear they're coming out with a 300w model.
The LCD should come with a cigarette lighter adaptor thing for plugging into a car (12V). This will help regulate the power. Just cut off the lighter adaptor and wire the wires to + and -.