The most common reason people give for wanting to idle all night is to run the heater or air conditioner. This can have serious effects on the vehicle's engine:

Idling for one hour every day for one year is equivalent to 64,000 miles of engine wear. – source

Idling accelerates engine wear and tear creating a need for more regular maintenance and an increase in the number of oil changes. – source

Because the engine is not operating at its optimal temperature when idling, fuel is only partially combusted, leading to fuel residue buildup on the cylinder walls. This can further damage engine components, including spark plugs and exhaust systems, increasing maintenance costs and shortening the life of the engine. – source

In addition,

• idling can result in CO poisoning
• Direct-injected gasoline engines can be carbon-fouled by idling

In the long term it is more practical to heat with a propane heater before bed, and a contact heater and appropriately-rated sleeping bag for sleeping. People in very cold climate may want to install a vented heater for overnight heating.

Air conditioning will require a generator or access to shore power.

In addition to the problems listed above, idling to charge is hard on the alternator. The alternator depends on sufficient RPM to spin its cooling blades, and airflow from the forward motion of the vehicle. Neither cooling method is available while idling.