I did the same thing: carefully removed each ceiling panel and labelled them with a number and direction so I could put them back in after insulation. Then I thought about it more and tossed the panels in my scrap metal pile! The good scrap metal pile, that is. The one I pull from regularly.
The reasons I decided to go with a plywood ceiling and wood ribs are twofold.
One, adding a reasonable thermal break to keep the metal panels off of the ribs will change the curve of the sheet metal. None of the screw holes will line up after this. Even a thin piece of rubber will be enough to offset the screw holes.
Two, wood has much lower thermal conductivity. Even with a thermal bridge between the ribs and the steel you'll still be passing lots of thermal energy through the seventy thousand screws, which will then pass through the sheet metal. Each one of those screws will be dripping when the dew point is right.
Also, wood just looks nicer
(subjective, I know)