If the battery is charged to 12.6 volts and the panel is working now (without being on shore-power) your 12v circuit is powered. That means the 12v lights will work, along with refrigerator on propane, furnace, and water-pump if turned on.
So what now are you expecting to work?
Nothing that plugs into a 120v,ac, outlet will work. That includes air-conditioner, micro-wave, televisions, etc.
You mention an inverter (converts 12v,dc, to 120v,ac). Do you actually have one and have located it? Did the seller say the RV had an inverter and show it to you?
If an inverter was installed it most likely is small and only intended to power the main television. It may have up to two 120v,ac outlets and located in cabinet near the TV. It has an "on/off" button and a fuse on rear.
In order to work the two wires on back must be connected to a battery, TV cord plugged in to unit, a good fuse, and inverter powered "on". Larger units are also grounded.
