Find any parkinglot marked with a white P in a blue sign on the map. Drive over to the parking spot itself and position your truck correctly. If you're at the right spot you get a pop-up saying press F (or the key you set it to) to turn off the engine. Then press enter (or the key you set it to) to sleep.
The achievement should unlock afterwards.
An example of the sign:
http://images.myparkingsign.com/img/lg/K/Parking-Sign-K....gif