Two ideas: Lean the trailer to one side so the front hatch ledge is on an angle to drain. Tape the hatch shut with foil tape. It will last a Winter and if there is any residue, when removed, you can easily clean it with mineral spirits.
The main detriment with covers is that they loosen over time and then the material, when windy and flapping, has a chance to abrade the surface under it. There was just a thread in the "Tech Issues" section of the Forum asking how to repair a roof edge because of cover damage.
