Cool use of a Chrysler Firepower engine

They used a "chopper wheel" to generate the sirens frequency, not a compressor into a horn. They tour on a trailer to shows. I can see propane being used as sitting fuel for a month is bad in anything. We start our diesel generators every month at our central offices for phone backup. IIRC diesel is very stable over time if kept airtight.
Diesel needs to be treated for green slime if stored more than six months or so.

Twice I have mothballed my Peterbilts when freight rates took a dive or fuel prices hit $4.00/gallon. The first time the truck sat 12 months and I was plagued by plugged fuel filters even after treating the fuel. The first 5,000 miles I must have changed the filters a dozen times.

The second time I pretreated the fuel and the results were better but not perfect.