I use a doubled up twist ties to tie the "pivot bar" to the edge of the shelf below. That keeps it from vibrating up and out of the slots.
Untwist to put it down. When it is time to travel, put it back up and twist tie it in place.
It seems kind of crude, but it has worked great for years.
Chris and Pat
2016 Ram 3500 Cummins Aisin Dually
2017 Cedar Creek 36CKTS