I use my Tracker custom cover when trailering. Towed twice without it, once in sun and once in the rain, and I'll NEVER do that again if its gonna rain. It took too long to dry out and clean the road scum off of everything.
The cover that I have fits very well, except that it rubbed the shine off the motor cowling where there the cover touches. I cut to length some pieces of foam pipe insulation, and then cut a slice down one side, to place over the windshields. I also cut up a cheap sleeping bag pad (1/4" stiff foam), to place in spots where the sharp edges of the boat come into contact with the cover. I also retract (or even disconnect) my trolling-motor so that the propeller blades don't come into contact with the cover. Mike W, that's a great idea about using a towel.
Once I'm on the road, I check the cover at each stop and tighten up any straps that have come loose. I found that if you tighten the strap with the tag end in a knot underneath the buckle, it doesn't come loose. Take the tag end, loop it back around the main strap and then back through itself. Pull UP to snug it up against the buckle. If the cover gets wet, it will need to be snugged down a bit more because it expands.
To me, the cover is worth using when I tow. I store the boat in the garage, so I don't have to use it as a mooring/storage cover. If it only lasts two or three seasons.
The biggest con in using a cover is that you have to store it dry or it will mildew. Fining a place to spread it out to dry can be a hassle.
