Once you've watched the movie are you leaving it on your iPad and why? All I do is download the film to the iPad and after watching it delete it from the iPad. If it is a movie I purchased I can re-download it later or do a transfer from iTunes via my Mac and the external drive I store iTunes material on. I see no reason to keep a movie on my iPad after watching it, unless I plan on watching it again in the very near future.
When I go out of town, I will download a few movies to my iPad, watch them on the plane or whatever and then afterwards replace them with something different or just delete them. When I have a good wi-fi connection i just stram the film from Netflix.