I've had Progressive for a number of years and have been very happy with them. However, the last few years they have been jacking the rates up on their RV coverage and many RVers are starting to move away from them for that reason. I found a number of satisfied owners on the Tiffin RV Network board that recommended Twin Peaks Insurance - RV Insurance Specialists
I checked them out and they have much better coverage, with full replacement value and diminishing deductible for significantly less premium than Progressive. I recently placed my coverage with them.
They also had a special glass coverage option that I chose. My normal comprehensive has a $1000 deductible. My one piece windshield runs close to $2,000 (I replaced one on the last coach once - ouch) so any time I need a new windshield it runs me $1,000. With this special glass coverage I only have tyo pay a $100 deductible for glass. It costs $59 extra per year but the difference between a $1000 deductible and a $100 deductible is $900. At $59 a year that's equal to 15 years to break even and chances are I'll have 3 new windshields by that time so it's a good option to have - especially if you travel on gravel roads from time to time.