When we got our Westfalia, the bottom layer of the two-layer
skylight was severely cracked in multiple places.  "What could
anyone do to crack the inside of a skylight?", I wondered.
Shortly thereafter, I was lowering the pop-top, and, standing in
the natural pop-top lowering spot, felt the skylight go "Crunch!"
on top of my head as I pulled the roof down.  Then everything
made more sense.

Eventually I cut out the bottom layer of the skylight completely, and
used some silicon sealer on the cracks around the outer edge of the
upper layer.  Less insulation, I suppose, but it works and looks fine.
I even get an extra half inch of headroom.

                                       -Steven Sittser