The cover itself is well constructed and performs the desired function.  I will offer a few suggestions to improve it:  

1.  Any other color besides brown.  Come on man, why not gray, black, white, navy ... really anything else.  

2.  Weights or tie downs.  In windy conditions, the cover is constantly flapping allowing snow or debris under the edges.  There has to be a way to keep the corners and sides down.

3.  Single person on / off.  It takes two people and two ladders to get the cover on and off.  Options for how to use with only one person would be a great feature.