After 7 rock-solid years, we did it!
Backstory: I had her family lure her to the drive-in. I arranged for them to play a video I had made right after the first main film. Our families and I were hidden in the back rows and surprised her when the video started. I proposed right after it ended and SUCCESS! She's so beautiful. Here's the video (I'll upload another version soon with her reaction):
http://www.youtube.com/watch?v=-B_IxeVNZ8s