The wiper blades that came stock on my Ford E450 RV were pretty crummy. They didn't work well and seemed a little small for the windshield. I purchased the Rain-X Latitude 2-IN-1 Water Repellency Wiper Blade. I replaced the stock 20" blade with a 21" blade.
The old blade just unclips and the new one snaps into its place.
Even going with a slightly larger blade they still fit well and cover more of the windshield when in use.
The Rain-X has held up so far. It is excellent at cleaning the windshield in the rain. The 21" is just big enough to make a difference. When its time to replace I may try a 22" on the drivers side and leave the passenger side 21".
Purchase Rain-X Latitude Wiper Blades on Amazon: http://amzn.to/2nM28LH