The sail panel is the upholstered board that is between the rear side windows and the back window, above the package deck, below the ceiling/headliner.
If the panels are in good shape, recovering is a snap.If not some new boards can be cut and the whole thing can be replaced.
Look in the interior upholstery threads. I think Dan Two Lakes has some stuff posted there.
I am recovering my bucket seat at the moment and I found his tutorials to be very helpful.