I've been looking into something similar. Keep in mind that most of the USB chargers ive seen on ebay and at Jaycar have a 1.0A and a 2.1A slot (or they might advertise 3.1A shared across two slots). Such a config wont charge 2 ipads. Ipads need a 2.1A slot. Even if you want a faster charge on your mobile, chose the 2.1A slot.
So if you're thinking of throwing a couple of these USB sockets in the back seat for the kids, make sure you get 2x 2.1A... otherwise.. "are we there yet?" ... "are we there yet?"
Im looking for something like this in a dashmount config - http://www.jaycar.com.au/Power-Produ...arger/p/MP3666 May be able to pull the guts out of it and refit it to one of these http://www.ebay.com/itm/Car-2-1A-Dua...3D131492692357