Just remember for them to work when needed generators must be tested and maintained. Diesel needs to be tested and treated. Then with propane you could have delivery problems and a tank to hold that much would be large and expensive.
Had one customer location with the big diesel back up generator set up. Would work mostly fine during routine run tests. When the transfer switch tried to spin it up automatically, it would usually fail. Took way too long for the vendor to find that bug but at least we had juice. In this part of the world propane is very common in trailer parks, weekend homes and warehouses so keeping the tank full doesn't sound like weakest link in the plan. As far as I can tell from running fork lifts, ya get about the same mileage from the same size tank NG vs propane.
Diving down the rabbit hole for a bit: Looks like above ground tanks range from $500 ish for 120 gal cans to $1500 for the monster 500 gallon. Not horrible in the context of what the generator and xfer switch is gonna cost. Retail residential propane is about $2.50 / gal right now. Generac says an 11kw generator will burn 2 gal/hr at full load but ya really gotta dig. Lost interest before getting to the answer about gallons per KwH based on fuel type. Rough estimate to run my entire house (electric heat pump) on propane looks like $8-10k installed and $8-10 in fuel per hour. Bugging out for a hotel with power is way cheaper.
