Seeing a movie outdoors used to be pretty simple. Drive a bit, pay at the entrance gate, find a parking space, and wait for the towering images to flicker into view. Some nights you’d even get a double feature. But finding a drive-in isn’t easy these days. Just 370 remain in the U.S., down from a peak of nearly 5,000 in the 1950s. What to do if you yearn to experience the cinema outside? Create it yourself. For that, you need five elements: the power to drive the whole setup, a video source, a projector, a screen and a sound system.