Cross seeding is so easy, see the rutorrent image above^

In the add torrent box you can see a button with 3 dots on it ... Underneath the red X button.
Click the button with the 3 dots on it then x out of it, it's that simple.
This will add your file directory and point the torrent to the right place, after you do that all that's left is to find the exact same torrent on two sites.
I usually DL from TL as I have a huge buffer there, find the same torrent on let's say SCC and make sure the name and file size are a match: there might be a few MB in the difference sometimes but this is ok.
Once you find the torrent on SCC just add it as you normally would, if the file is the same as the TL one it will say "checking" instead of "downloading"