We had a Jayco Toy Hauler TT that came with a cushion that was something like 6" square and RV queen-sized wide. We never knew the exact reason for it, but we presumed that was exactly what it was for - to extend the length of the bed.
With my wife being 5'2" and me 5'11", we never needed/used it as it would have made it difficult to walk past the end of the bed with it in place, which was required due to the layout. So, we just stored it until we sold the TT to get our current rig.
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