If you're going to do plywood id do this between the plywood not lining it with deadner..
https://www.sounddeadenershowdown.com/products/extruded-butyl-rope-ebr
Strech it out 2x its length and apply it to every part of the roof braces the plywood will touch. As for the cld tiles to stop potentual ringing use the 30% of the deadner to the squared area of the panel that you want to reduce the ringing on. Btw id highly advise you drill and tap the screws into the sheet metal its 2x stronger.
If you want reduced flexing vibration and ringing this is the proper way to do it.. you can order some head liner and put it on the plywood. Id use the thickest ply you can.. fyi it will save you hundreds and bracing/integrity is tge key to numbers!!