We do not have an APU so must idle to stay cool.
The owner of our repair shop in Florida swears that you would be better off putting the 10k into an interest bearing savings account and keeping it for an engine rebuild when it becomes necessary. He claims that the APU's break down and require too much maintenance and upkeep to make them worthwhile unless the fuel goes over $4 per gallon.
Your repair shop owner might be interested to learn about Onan generators. We purchased ours new with the truck in 2003 and have 8,000 hours on it now. In that time, it has been in the shop once for a repair. That was in the first month. A defective fuel pump was cheerfully replaced under warranty at no charge to us. Otherwise it has been trouble free, unless you consider oil, filter and coolant changes trouble. I do those myself so the only cost out of pocket maintenance cost is for the oil, coolant and filters. There is no down time for maintenance as it is done between loads when we are in service or done when we are out of service for other reasons.
Oh yeah, I almost forgot. The drive belt gave up the ghost somewhere around 6,000 hours. Having a spare in the truck, I replaced it myself.
The fuel pump repair was made at one of the dealers in the nationwide Onan dealer network. It was in Salt Lake City. They got us in immediately and we waited one day for the part to be overnighted in. We have visited several Onan dealers over the years to buy filters and a replacement belt. The facilities are easily found, modern and clean. They serve the high-end RV market mostly. It's more pleasant dealing with them than many truck dealers.
Eight thousand generator hours would equate to 8,000 hours of engine idling if we did not have the generator. At a gallon per hour for truck engine idling, that's 8,000 gallons of fuel or $24,000 at $3.00 a gallon. The generator uses fuel too, but nowhere near a gallon an hour.
At $10,000 for an Onan generator and 8,000 hours of truck engine idling wear and tear saved, it's hard to figure that you would be money behind by buying a generator.
We would buy an Onan generator for a new truck again, even if fuel was then selling for $2.00 a gallon. Anti-idling laws are enforced here and there at least. I like the freestanding electric power source the generator provides when I am running electric tools to work on the truck. And I especially like letting the big truck engine rest.
