I drive for a guy in the winter and that's all he uses.  We haul sugar beets and beet pulp in the winter months so it is almost a necessity to not have bows.  My experience is with Cramaro and Shurco.  They both work fine.  The last 6 sets of trailers my winter boss has gotten has had the Cramaro's.  I don't really know why he went that way.   The shuroco's he had always worked fine.  They crank pretty easy even when it's cold.  He also runs mesh tarps with just one back bow to pull them to the back.  If water doesn't bother you those are cheap and easy to make yourself.  Just some pulleys, shaft, cable and a tarp.