My ex-wife had a singe 12" with amp mounted to the box in her Accord. I used a standard replacement 120V plug set for the power, ground and remote. It was a low-power setup that only needed 8 gauge wire, which was the maximum that would fit in the plug ends When we needed to remove the sub box, we just unplugged it and the RCAs and took it away.
Something like these:
If you only need to disconnect the speaker wires but keep them protected from shorting, you could use the non-grounding version of these.
Or, if you want it to be slick, flush-mount something like this into a side panel and run your wires concealed to the amp and run a length of 12 gauge extension cord from the box to the outlet:
I'd look for a black one, though.