I use a cover while trailering... I had a custom cover made with a very heavy duty material (I can't remember the fabric name right now...)
I try to keep all water out of my boat, to minimize any rot. Since there is no infiltration through seams in the hull, I don't want to get stuck in a rainstorm and have water come in, only to seep into cracks inside..
I also do not want to get the windows and hull sandblasted with stones and flying tar/bugs/etc.... and it keeps the inside free of dust.
The cover I have, is one piece, and it keeps all moisture out. There are several vents to allow circulation. There is a drawstring that cinches up around the shear plank, and has straps with clips to attach to the trailer frame. it is custom fitted for my windshield and bow/aft light, and is reinforced around the touch points... like the window corners, horn, spotlight, etc.. I does not flap much at all on the road.
I usually use some scrap tee shirt material to soften any abrasion , but it fits so well, that I dooubt there is much there anyway.
When it is parked outside on vacation, I run the wheel jack up, and any water that hits the cover, rolls off the back and off by the motor, with nothing going inside.
The only thing that I don't like, is that I should have asked for white straps... Although black looks better, it sometimes leaves marks on the white hull (like a nickle scrape). They mostly come off with dish soap on a paper towel.
Here is a pic..
