Must admit, having a little experience of correx through work, I have my doubts if it will be sturdy enough to stay in place without buckling (especially in just 2mm thickness). But it may do. And I definitely agree side-to-side for the ribs!
I also wonder, bearing in mind the fabric (which as we know is quite stretchy) still has to be glued on, whether in time it still might come unstuck from the correx and droop down? Given that the two of the main causes of the problem seem to be gravity and extremes of temperature.
The most durable Excel roof lining I've experienced was on my SA, where the previous owner had covered two pieces of thin hardboard with magnolia leathercloth, and all the roof rails to match. Far as I could tell, the flat panels were just held in place by the rails (the back one did extend an inch or so onto the front panel, presumably for a firmer hold by both upper edges of the centre rail rather than just the back edge). But it did mean that through my whole ownership of that car I never had to even think about headlining, let alone worry about it. That just came with the last two examples!!
I'm looking forward to the results
