You are in a fortunate position - you can make stuff available (this is nice and generous) while hardly having to upload anything. Consider joining a private tracker that gives you credit for TIME seeded, not Gigabytes of seeded material. Then just keep the stuff you download in the download folder for a long time before moving it/deleting it.

Nice. In my experience you'll get a few hits a year, but enough rare torrents and you'll be seeding almost continuously