When I had traps on an old lease I always kept the door wired open when we weren't there and did this initially for a couple weeks prior to setting. I also had a feeder setup right over the top of it in a tree. Good luck.
A feeder over the trap is a good idea. Here's a setup I put out where I hunt. The feed sacks force most of the corn to drop directly into the trap, keeping it baited when I'm not there. I've since replaced the paper bag material with some pieces of plywood.
As a side note, this is a home made feeder I put together out of bed frames and a molasses tub. By the time I bought a funnel, varmit-proof cage, spinner plate, legs, and (at a garage sale) a used controller, I could have purchased a cheap one ready-to-go from Academy. While I enjoy DIY projects, I won't be making another feeder any time soon.