Booster cushions came with our 2017 Chateau. It took three of us, including the Salesmanager at LaMesa RV in Phoenix to figure out what they were at first.
If you can’t get them from your manufacturer, you might be able to get them from a place that does Marine upholstery type work. Ours have some kind of flap to keep them from sliding around, but otherwise they are a pretty basic shape, just made of a much denser foam than I’m used to seeing at some place like Joann’s.
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