The dreaded head liner sag

[LesZapata]

I'm ready for the fabric, but I'm not 100% sure what type to apply. I have so many ??????????????????????????????????

The fabric has me worried it'll stretch with moisture and time, so I thought of imitation leather, but then there's heat. I live in SoCal. I don't want to do all this work and end up with a big failure.
Also, what size foam did you use?

[Vetruck]

A tip: There were two rear clips that are hidden holding the backing to the roof. Once you remove the rear dome light the rear is released by moving the entire backing panel towwards the rear of the car about 1 1/2"/ Do not try to pull down on the rear until you slide it backwards in direction.