APU or Generator

[Chamberpains]

How much are you idling? What region or area's do spend most of your time?
Idling isn't always bad. If you never idle enough to justify 10-15k $$ for an apu plus upkeep, then idle away. I personally don't have 1. Never did. I carry a Honda generator and a space heater for the Winter. In the summer, I just idle till it cools off. I look for shady places to park. Use fans.
If your in the frozen north or the burnt south all the time then you may want to opt in to an APU. But even then, do the math.
You can get your engine tuned so that your idle fuel use is minimal. APU's sound nice but I can't see hanging another chunk of expensive metal off my truck without it completely paying me back.

Just some quick math.
$10,000 (cost of APU) converted to Gallons of fuel (say $3.50/gal) = 2,857 gallons of fuel you can buy.
Take that number and divide it by how much you idle a day (lets say 10 hrs/daily @ 1 gallon per hour. Most trucks are less, closer to .7per/hr but 1 is easy to work with) = 285.7 days of idling
Most guys only work driving 5-6 days a week (lets say 5 days) = 57 weeks of idling.

Thats over a years worth of idling if you're forced to idle that truck every single day your in it. Most guys own their trucks are tougher than company drivers because they know they save money by not running the truck plus half the time it nice outside so they brave some slightly uncomfortable temps .... That really extends that time frame of a little over a year out a ways before you get your money back in saved fuel.
I didn't even throw in the fact that the APU burns fuel and has maintenance costs.

Always do the math. Your running a business!!