I used one of these for my Ritter 20x24. Worked great.

https://www.thule.com/en-us/bike-tra...e-2-_-10203022

While you can always find them for less than retai, it was a drop in the bucket when you add up the price of admission to 20x24. Heck, it didn't cost as much as a box of film when I bought it.

Mike