You should really install your inverter very close to your battery and then run a 120v extension cord to your appliance. 30 amp DC really needs an 8 ga or heavier wire to avoid too much voltage drop and I have never seen a 12v lighter plug that will handle it. You need to look for a trolling motor plug and socket to handle the current and heavy wire. If you need to run more than 6 feet of DC wiring you should go to 6 ga or more.
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