I have a boat cover, it's not the one for the boat so its kinda big, but it's perfect for my winter or non use storage. I use 2 plastic saw horses and a 2x4. I have he saw horses facing front to back and the 2x4 on top of that. The cover is the perfect size to fit over the raise support and the motor, then I just tie it off to the trailer with tarp ball bungees . I cover that with a tarp, and i use the tarp ball bungees that fit thru the holes and tie those off to the trailer also. So far it's held up great with the snow storm and wind storm we've had up here lately.
http://www.homedepot.com/p/Sigman-6-in-Tarp-Ball-Bungee-25-Pack-BB06B/203217327