We have a Pinnacle with single pane windows. Our previous fifth wheel had dual pane. After 4 or 5 seasons they started to fog. They are not comparable to a sealed window you have in your home and as stated are just 2 panes of glass. I think they do help some which is common sense but we didn't want them again. We've had our Pinnacle out on some really hot days and I did have to close the shades where the sun hit the windows. We didn't have any problems keeping it cool.
Look up the Josh the RV Nerd at Haylett RV in Michigan. He has some really interesting videos, including one on the dual pane windows. He is also a Jayco dealer.