If it is primarily for slip use, make sure the fastening system is designed for that, and not for walking around a trailer.
I would go for a fabric like ripstop, that you can cram into a stuff sack, not a bulky sunbrella type.
Here's an example for you to think about.
I just had my local canvas shop make me one. Used d-rings and straps to attach to the hard top bracket to flow under the rocket launchers. I had to add some hardware to the transom.
Sides hang with sand bags so I don't need to use fasteners, but when on the trailer I could put some webbing under the hull.
Zipper near the transom door so you can access without undoing a bunch of straps.
I put it on last week on the dock, works great.