Delmanation repair help needed

Im repairing a delaminated side wall and im trying to find the best adhesive to glue the luan to the foam and filon. I was considering using 3m 30nf as an alternative to stabond which is extremely expensive. Has anyone used 3m and had good results. My second question is what kind of backer is used behind the filon on the front wall. It does not look like plywood it looks more like cardboard.

Thanks