Pro's and Con's to slide covers.
Personally I don't have them. It was quoted around $1,200 for my 3 slides. I debate back and forth about spending the money.
I have a broom with a tilting head and cut at a 45 deg angle with a telescoping handle I got at Aldi for around $10. I can stand on the ground and sweep off the top of my slides.
http://www.alibaba.com/product-detail/Telescopic-handle-brooms-and-brushes_662685608.html The handle is like 12' long when open.
Con: They can flap in the wind and some claim if it gets cold, they can freeze and not roll up right. IF something does blow up in there you may not be able to see it or reach it to remove it. Harder to inspect and perform maintenances on you top seal.
Pro: Keep the sun off the slide and helps keep slide area cooler inside. Debris can just roll off when you close your slide. Read you need to replace the material part every couple of years.
You are suppose to wipe the inner and outer seals down with a UV protector/lubricant twice a year and lubricate the slide mechanism. Honestly I have it done in the spring and fall when I have the RV serviced. Since I have an extended service plan with my dealer, I have them to all the maintenance. This avoids any questions about if it was serviced correctly. If they performed all the maintenance they shouldn't be able to claim it was not done correctly
Well, that's my 2 cents