@szerby: we have had the headliner installed for about 6 months now. We installed them in Oklahoma, but have since moved to Missouri. We have not noticed any shrinking of the panels like what you describe…but the temps have not been excessive (comparative to the southwest).
However, as an update to my previous post about the headliner installation: While I kept it out of direct sunlight and covered while not in use, the ambient temperatures (highest mid-90’s) have been hot enough to cause the glue on the HD velcro pieces to melt, causing the panels to detach and bow in some areas. There doesn’t seem to be any damage to the panels or shell. It is a minor inconvenience for now, but we definitely plan to re-attach the panels with a more permanent solution (thinking the 3m 77 stuff). Also, as someone else pointed out to me, the gap between the panels and shell still results in condensation, but it is not a large concern due to the epoxy on the inside. Live and learn.
For those still considering how to mount the headliner, the velcro did allow me to achieve what I wanted – it just didn’t have any durability.