Class A's started going all electric more and more years ago and we are now seeing that trend move down the line to Class C's. It is now well know that you no longer need propane to dry camp. I still ...
I suspect that backyard grills and heaters consume far more propane than RV's. Some new class A's may be going all electric but unless they install a hydronic heating system there will still be many with propane for heating and hot water.
I've only looked a few class c and b but they all had propane for heating and hot water and the smaller ones were only 30A power.
Propane is everywhere so it's no problem finding it.