I bought 150W inverter with USB port from Discount Auto Parts for about $20. What I liked about it is that it have fan and it will automatically shut off if battery voltage drops to 10.5V.
It was disassembled and wired for external switch and status light. It is sounds more complicated then it is. All you need is disconnect wires from internal switch and status light and extend them outside.

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I used 10 gage wires to connect it directly to the battery.
Depending on how big is your inverter and how far you will run the wires, you might need to use different cable size.
Here is link for the reference:
Recommended Power and Ground Cable Sizes
15A fuse installed. (ALWAYS USE FUSE!). Install fuse as close as possible to the battery.

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Here is positive wire connection point:

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Here is ground connection point:
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Secure Inverter with zip ties under the glove box.

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And the last step connect USB and AC cable to the inverter tuck all the wires ( I used black duct tape to secure wires to the firewall ) and you done.
P.S. In my case, one of the USB ports connected directly to the back of my Pioneer headunit (which have USB port in the back for IPod controls).

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If anyone have any questions, please feel free to ask.
CUBE