I have..like three or four extra USB outlets not on keyed power. They are just on a fused power lead from the battery. The ones I have do have an on/off button that lights the LED when on so I know it's powered on. I use them for the cameras and GPS tablet so they always have power when I stop for a while. I also have a dual fast charge USB adapter in the glove box for the keyed cigarette lighter/Acc port if ever needed.
Any of the existing ports can be made full-time power by just clipping it's power supply and re-routing it to the battery but remember to always use an inline fuse right at the battery..very important. And know that if you leave something plugged into it using power...it will drain the battery in time.