Slide out tips out while driving

[Mel]

I have a 2009 Montana 3400 I purchased new in February 2010. On a recent trip twice I saw in my mirrow the top of kitchen slide out tip out at least a foot as I was going around corners. I about panicked. Took the 5th wheel to a dealer where I was vacationing and they checked it out and said everything is OK. Suggested I cut a board and use to block the top of the slide out and keep it from tipping. I can do this, but it seems like there should be a better solution. Anyone faced this and what did you do?

Thanks for any help.
Mel