I wanted to do exactly what you want to do. Watch TV and videos off-grid.
I ordered this inverter:
Inverter Link on AmazonI ordered this USB outlet for charging:
USB 4 Port OutletThat inverter has provision for a remote on/off switch. No need to interrupt power to the inverter, just turn it off with a remote switch. This inverter is a pure sine wave. I tried a MSW plugged into the 12VDC outlet, which I do have one, but no go for our TV. A PSW is not expensive, so why not treat your electronics to good tasting power.
That USB outlet is a 12VDC, which worked for me because I had a 12VDC source in that wall. If you don't, you can get the same outlet in a 120VAC version.
The inverter is in the storage compartment. Had to run a few wires, but it wasn't any big deal to do that.
Ended up looking like this:

The Ivory outlet is the original and is still on the house power. The TV is currently plugged in to that in this photo. When we move off of shore power, I move the TV plug to the White outlets and hit the White switch to power up the inverter. The USB ports are live all the time, on or off the grid.