Has anyone used one of these? I know you get what you pay for, and this is a real cheapy from Harbor Freight but I'm considering it for two reasons: 1-I'm planning to spray Rust Bullet with it so it's a bit sacrificial and 2-I will likely be laying on the floor spraying this on the bottom of my car so I don't expect a gravity feed would be all that effective. Any thoughts on using this particular gun or one similar? Also, where can I find other guns like this, if it's a way to go? Any thoughts?