My friends have been doing a guerrilla drive-in by all driving up to the back of a closed down business off of the highway, projecting a movie onto the (white-painted) brick wall and using an FM transmitter for the audio.

The projector plugs into an inverter and projects through the windshield. We're still trying to figure out how to all talk to each other during the movie. So far, cell phones with earbuds and microphones seems to work alright but anything on speaker phone gets feedback.

The projector is something like 65W and is powered from the car on idle. It'd be nicer to run it off of batteries but that can get a bit expensive.