I have a decent cover over my stock mooring covers. It's made by Classic Accessories and cost me $164 on Amazon. I reccomend it. It has weared well.
They have different sizes, so the fit is really great. So don't just get a $100 "universal" one. Get one that fits for $60-$70 more, it's well worth it.
It has two breathing outlets toward the back for air to flow through.
It's said to be "trailerable" and I can confirm that. I do use it when I'm trailering.
It not only has the stretch fit hem, but also several built in straps that I attach to the trailer frame.
I have an 18 foot bow rider, so my mooring covers are one for the bow and one big one for the cockpit.
Like any cover, you need to make sure there's no puddling. If you find there's a low spot, stick whatever you have under there to prevent that. It may need an expandable pole or just a cushion or blow-up tube.