An apparatus for sealing such a gap may be a plunger seal which may include a flap arm comprising resilient sheets and a wall arm comprising resilient sheets. A proximal end portion of the flap arm may include a closeout seal coupled to the flap. A proximal end portion of the wall arm may include a plunger having a geometry corresponding to that of the closeout seal so the plunger may be matingly received by the closeout seal. When positioned in a gap, the plunger seal may exert a force to urge the flap arm towards the flap and to urge the wall arm and resilient sheet towards the structure to seal the gap.