I store my touring kayaks (HTP(two)and thermoform) outside on Talic sawhorses see their site for description), using Seals cockpit covers and Danuu kayak covers. I'm not really that big a fan of homemade solutions. The Talic sawhorses were about seventy bucks, the cockpit covers are the same as used for transport, and the Danuu covers were (I think) about a hundred).
In about seven years of using this system, the only damage I've ever had is when something (or someone!!) chewed the front toggle off my Kodiak - I had been too lazy to use the Danuu cover that week. BTW, I live in NW NJ.