I agree with what others have said.. your ultimate inverter choice will require some knowledge of your electrical loads and desired style of travel. What size house battery system does the bus have? What are you needing to run while not plugged in or running off a generator? What features do you want in your inverter - charging, boosting, pure sign wave or modified, etc?
With the heatwave ramping up, I doubt you'll be enjoying much dry camping inside a metal tube anyway
We bought our bus this time 2 years ago in southern AZ, and it was ... not fun.. weather wise. The high on the day of our first long drive from Yuma to Lake Havasu was 127. We had no house battery system at all, and no way to run an AC when not plugged in.
We picked up our bus in Yuma, went to the nearest campground with 50a hook-ups, a bathhouse and a pool, bought a Passport America membership and paid for a week at 50% off. And then we dug into learning all the new systems and figuring everything out. And then we did as Clifford suggested... retreated to Flagstaff to cool off after baking our brains for a month.
After getting our bus settled and getting a feel for it.. we then designed our house electrical system with a boosting inverter that could run a roof AC for a couple hours off grid, with a battery bank to match. An off grid electrical system requires some serious thought, planning and investment to find your ideal balance... don't rush if you can avoid it.
For your initial time... I'd suggest getting to the bus and see what is there, and what you'll absolutely need to get through the initial days. If there's a 12v outlet, you may find that picking up an automotive 400w or so inverter is enough to run things like a laptop and small items. And you can pick that up in any truck stop, Walmart, Radio Shack or Harbor Freight.
Best wishes... it's a fun adventure to finally get your first bus! Excited for you!