Why use the inverter for your USB charging needs? I installed 10 west marine USB charging ports all over my camper. They wire straight from the battery bank (via a fuse box of course). Best bet is to run as much off straight 12 volts as possible. You waste a lot of juice in the conversion process, and for USB charging it's kind of silly to go from 12v D.C. To 110 as back down to 5 D.C. The USB ports are the same size as the cig outlets and you can even get a set up from Amazon that has both style outlets on them. Just hook up a power and ground wire to them and you are good to go.
Here is one of my charge stations on my kitchen counter.
Also, 12 volt LED flat screen was pretty cheap on Amazon as was the DVD capable car stereo with av outputs.
Moderator edit to re-size pictures to forum recommended limit of 640px maximum width.