diesel class c

I did a quick research on the major Sprinter-based class-C manufactures. The 3600 watt propane generator comes standard. The 3200 watt diesel generator is optional. I imagine buying a new one off a dealer's lot, you'll get the higher wattage propane version.

Regarding excessive idling of the Sprinter, Google this.

"Mercedes Sprinter idle warning"

You will get many hits on the topic. It does seem to be controversial. Make sure you understand your specific Sprinter idling limitations, if any.