One way to combat extreme heat and low humidity is to grow the plant hydroponically in one of those 5' diameter hard plastic wading pools that people often get for their kids or dogs. Put some gravel in there (don't need to fill the pool with it, just enough to stabilize the banana), get a cheap aerator, hook up some airstones under the gravel, and plant your banana in the middle. Add nutrients and you're good to go.
Your banana gets maximum water (without drowning, since the water is aerated), and also gets a bump in humidity by being located over the pool.
I used this method successfully here in Kansas last summer. We had extreme drought, with lots of days over 100F and very dry, dessicating winds. The one banana I planted in the ground withered away to almost nothing, but the bananas in my three wading pools flourished.
Here's something similar that someone shared on YouTube: