I have a WS8289. The kitchen slide is heavy due to the stove, refer, and couch. Pushing on the top of the slide will cause it push out. I had the slide tip open about 8" on a downhill hard right turn, even though I was only doing about 20 MPH.
I use two slide locks all the time.
Tom & Renée
2015 Wildcat 295RSX
2012 Ford F-250, 4x4, 6.7 Liter Diesel