I just recovered my saddle last night. I started with a Selle San Marco Island...
Pulled out the staples and peeled away the original cover...
Roughly traced the cover on marine vinyl (allowing 1/2" excess on all sides) and applied spray adhesive to both the saddle foam and the back of the vinyl...
I had to bind the rear with twine and tape to hold the vinyl into place until it bonded to the odd sahpe on the rear of the saddle.
After a few staples and adhesive the saddle now looks like this: