This all started when I chanced upon an old racing saddle I found at the local community recycling co-op. It turned out it was an old San Marco Concor saddle, as used by the pros, Armstrong, Contador et al. However the cover was quite shitty but the shell itself was in pretty good nick. Being the kind of guy that I am, I decided to recover it. It took a while, rummaging in my local spotlight before I could find some decent faux leather vinyl.
Here's how it started with the original cover ripped off
Step 1: Lay some vinyl or other covering flat and wrap it around the saddle so you can trace the outline onto the inside
Step 2: Check the outline before you cut it out, then cut out the folds along the curved edges so you don't get too much overlapping material on the inside faces. I used some contact adhesive and some clothes pegs to get the vinyl to stick, a hairdryer also doesn't hurt to soften up the material and make it a little bit more stretchy.
Step 3: Finished :)