The bead board is a structural element, especially in the roof of a NL or Bigfoot. The structure is made up of the outside fiberglass skin, the core of bead board, and the inner paneling, forming a composite sandwich panel. When one of them or the glue bond fails, the individual pieces are quite flexible.
It might be possible to inject an adhesive through the fabric and panelling, but since both sides are covered in the contact cement they use, the new adhesive may not adhere very well to either side, sticking only to the failing contact cement. You likely have nothing to lose by trying it. The alternative is to pull the interior paneling down, clean up the surfaces, and re-glue.
It is a shame that BF and NL do not use a proper structural foam rather than bead board. We always hear about how these are"built like a cored boat" but in fact no cored boat would use bead board as a structural material. My first Bigfoot had extruded polystyrene core, much more suitable than bead board (expanded polystyrene) but still well short of a boat structural core which is typically PVC or SAN material and much stronger both in shear and bond strength. Bead board you can easily crumble in your hand. The issue for them is too much cost I guess.
