They are a storm pole to stop them swaying and steady them up. We do not have one on our 6 Dylan but Phoenix has one.
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Ours is a length of we think 3/4" box section. We have a u shaped bracket bolted on one of the hitch bolts and one bolted on the back wall. They have a hole through them which matches a hole in either end of the box section and a couple of pins holds it in place top and bottom. Phoenix had hers from new as far as we know.