That wouldn't work for me. I frequently go to Montana, and there are two speed limits. One for cars and big trucks, which is ten slower. The camera always reads the slower sign.
It would be a hell of a lot simpler to use a separate 100-watt LiPo battery. (WattCycle $160)
If you use the 12-volt AGM battery that's under the seat and suck it down to 12 volts or below, you'll kill it. And that would be easy to do with your DC fridge.
You'll also want a voltage step-up...