http://redoorninkayak.embarqspace.com/#/sprayskirt/4530714805

Here's John Doornink's tutorial on making skirts... Duane Strosaker used to have a guide also i thought, on rollordrown.com but his site seems to be gone.

Getting it to fit the lip is a matter of making a template tracing on paper or posterboard and outsetting the line by enough material to create a tunnel for the bungie if you are going that way, or enough to wrap the bungie if you are stitching right through it to make a non-adjustable skirt.

In my experience, a taut neoprene skirt will prevent the pooling of water in your lap on a keyhole cockpit, however it may allow some pooling behind your back. Since that usually correlates to the vertical seam on the tunnel, as well as the tunnel to deck seam, it can be a leak point.

In a smaller Greenland style cockpit, usually a much looser conical skirt is used that lacks the "deck" part of spray deck, but allows a range of movement unimpeded by a taut neoprene deck and body tunnel. Since the cockpit is much shorter than keyholes, paddle drips tend to land on the foredeck rather than the skirt (then again, Greenland paddles shed more water over the kayak), thus preventing pooling during upright paddling on smooth water. Add in chop, splashes or rolling however, and you can develop a sizable aquarium behind your back.