If I may offer an alternative solution... I recently picked up an automotive 4 port usb charging station, rated by china at 40 watts (yea right).
I cut the cig lighter end off and crimped on some quick-connects. Ran the cord down into the storage bay under my dinette that is home to my AGM batt-bank. Now I have USB power anytime it's needed, without having to run the inverter or be on shore power, and without having to hog my limited AC outlets with usb charger warts.
Saicoo® 8A/40W 4 USB High output