Good suggestions by all.
I run 120V entertainment devices with my 12V system, also a small dorm fridge. I have a vintage NAD receiver and two sets of small speakers in boxes, and a 32" LCD LED screen.
My gear is: 300 AH of battery capacity, a pair of GC2 Sam's club 6V's in one bank and a separate bank of 3 AGM telecom batteries totalling about 100AH. I use a Xantrex Prowatt 1000W pure sine inverter. Charging this is a 235W solar panel, an included DC converter, and whatever my towing unit will deliver. I also have a generator but for weekend trips, it stays at home. Everything is connected with 4 AWG, minimum. The connection between the 6V bank and the distribution panel is 1/0 welding cable, the run is 6'.
If you are going to rely on the 12V system to deliver inverted 120V power, you need to do the proper engineering to make it happen with an adequate battery capacity and the ability to recharge before draining batteries to a low level. I'd estimate that using just two 6v batteries over a weekend of audio devices, lights, and possibly other 120V devices will drain the 6V's below 50% SOC. That is the preferred level of discharge not to exceed. A solution would be to add battery capacity or engineer charging into the usage. Solar is a great solution as it uses no energy that costs $$. Starting the bus occasionally is another solution and removes the capital cost of solar but uses fuel. You have decisions to make about the system and a good first step is to break out a pencil and calculator to assess exactly what total power use will be used in a typical day of bus use.
Here is one calculator:
PV calculator
