you are correct. you should be able to feel where the backer is if you tap/knock on the wall with your hand.
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I am on this forum to help as I can, and am in no way the official response of Forest River, Inc.
On my 29hfs the backer runs from the corner to the bathroom door. Like JM said push on the wall and you will feel the resistance... Push down low for comparison... nothing there... But solid above.
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Hyper Lite was sold
2017 F-250 4x4 6.2L Gas
I can't fix everything, but I can make it so nobody else can