Can't the manufacturer install the cover before you take possession? You could search this Forum for `slide topper' and read all the reasons for and against one.
IMHO if one has to get up on a ladder or the roof in order to clean off the slide before retracting that's reason enough to get a cover.
Dick_B
2003 SunnyBrook 27FKS
2011 3/4 T Chevrolet Suburban
Equal-i-zer Hitch
One wife, two electric bikes (both Currie Tech Path+ models)