I am a lineman for a living, propane/natural gas is the best bet but they use a tremendous amount of fuel. My advice is to run for a few hrs and turn off. Continue this method. People freak about freezers and fridges when the power is out. Food will last for days if you don't continue to look in them and let the cold air out. They have an automatic transfer switch so when the power is off they automatically switch over. Lineman don't care about generators because we ground primary voltage lines before handling them to eliminate differences in potential. Best wishes...
We have had a whole farm PTO backup generator since the mid 60's. It's 42 KW. Not for your air conditioners or water heaters. Keep the pigs alive...When we installed it our local electrical coop had rules.