Solar panels are under one dollar per watt now. If you buy big residential panels in the 300 watt range they can be down around 50 cents per watt.
I don't really recommend lithium ion batteries for RVs but if you truly only have room for one that might make sense. Considering your light loads I would think your current battery would suffice. You may want a small inverter to provide 120v AC for the TV and other things. I would only get a purse sine wave unit. They too have really come down in price. Morningstar makes and excellent 300 watt inverter.
For a small charge controller there are many options. You don't really need an MPPT unit for a small system, particularly with only one panel. But, MPPT can get you more output from a given array. Blue Sky is my choice for small MPPT controllers.