Typical problem we all see in RV parks.

I can't explain the pickup trucks other than maybe trying to warm up the inside first. Those complaining about diesel motorhomes idling before leaving obviously don't have one. Mine has an airbag dump valve that lowers the coach about 6 inches when parked which makes it more stable but also drains most of the air from the tanks. In order to move the vehicle you must build up the air again because the brakes won't release until the air gets to about 70#s therefore you need to let it run to build up the air. I try not to leave too early so as not to upset my neighbors but idling to build air is a must or it won't move. I also can't move my slides while the engine is running so we raise the jacks, build the air so the brakes will release, shutoff the engine, unhook hoses and cords, bring in the slides, then start the engine and move off the spot and away from others to hookup the car.