Depending on the unit, most gasoline engines can be fitted to run on propane or natural gas. HP will drop about 20% on propane, and a little more on natural gas. There are also kits that allow you to run both in a either or configuration. That may be more useful with respect to long term operation and fuel flexibility.
In extreme cold weather, the propane tank(s) may need some heating in order to keep up with fuel demand.
