We also bought the ADCO cover; we have to secure it to the trailer hitch in the front and also to the rear (we have a spare tire mounted on the rear bumper) to keep it from flapping around in the wind.
If you do buy one, be sure to wrap something around the sharp edges (bumper, corners, etc.) so that the cover doesn't tear. I have been using leftover styrofoam pieces that come in boxes with TV's, electronics, etc. and taping them to the corners.
We're very happy with our ADCO cover. I read somewhere that you should buy one 2' longer than your actual trailer length (maybe on the ADCO box?).
We put the cover on after it was open a couple of times, and then figured out that it's easier to put the cover on first, and then open it up . No ladder needed.
We pad each of the lower four corners at each bed (upper shells) (we don't have an SL), and wrap the hold-down clamps at the bottom of the swing arms. I also put some padding around the license plate in the back. Also pad the lower four corners of the bottom TM shell and the ends of the bumper (ours is square).
Another thing I do is to roll up the flap where the door goes onto a pvc pipe (3/4" I believe) (I tape it with duct tape to get it started). I've found that it's much easier to keep it up out of the way of the door with that pipe in there.
Although we have tried to be very careful, we had to use the patch fabric that came with the cover soon after putting it on and taking it off a few times. So, I went ahead and ordered an extra fabric patch from the factory (it's a fairly generous size). Now, we have it available if we need it.