Natural gas gives even less power than propane for the equivalent volume but there is so much of it around. It once was burnt off as waste cause before pipe distribution systems it wasn’t worth the trouble to transport. A tank for compressed natural gas would have to be very large & or very highly compressed to get any range for a class C. We will see CNG as the fuel source for back up generator at home/business a lot more in the near future. We have seen when the power goes down for an extended time shortages occur cause of coarse cant pump fuel at stations that are without electricity.