Since it is small inverter and does not draw too many amps you can get away with using a fuse tap, seen below. You plug it directly in to your fuse block. If you put it in the right location (any location that is off when the key is off) it will turn on&off with your ignition. Sometimes you can find a extra unused fuse slot on the fuse block, if not use a fuse that does not have much load.
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