I bought a round greenhouse/gazebo from Willab Garden several years ago, and now we're thinking of giving it some love & extra care. The door has been a bit skewed from the beginning, making it difficult to close (without lifting the door slightly with the handle), but now it's gotten worse, so I feel I need to address it. I placed a square in the doorway and see that it's not perfectly straight there either. I took down the door to see if anything can be adjusted, but unfortunately, there's no room for that. I'm considering sanding down a bit at the bottom where it's catching, but the question is what to use for sanding aluminum?