Harmony spray skirt sizing

I am considering buying a Harmony Elite II touring spray skirt for my kayak, but Harmony has no sizing information on their web site. Neither does the vendor, although it comes in several sizes. Would anyone know what size in this skirt would fit a Necky Manitou 13? The cockpit on my kayak about 32"L x 18"W.

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check the outer coaming measurements of your cockpit, I found that the Manny 13 has a similar cockpit size to the Tsunami line but a little more elongated.