Why not just do things simple?



and so on..
No installation required.
Although, personally, you ARE in a "RV", and that RV HAS 12V run all through it..
I would just go with 12V to USB adapters and mount them away from the 120V outlets.. The advantage here is you ALWAYS have 12V power, not so with 120V..


You can mount those on a panel and add a toggle switch to turn them off when not needed to save battery..
OR..
Install a couple of cig lighter ports and use one of these..

Using the above ideas gets around the issues with the one piece 120V outlets..