A flanged vapor box for mounting an electrical component in a wall or similar structure while preventing air infiltration around or through the box. The vapor box includes a flange with an integral face gasket and one or more cable gaskets at cable entry points into the box. The face gasket prevents seepage of air between the drywall and the box. The cable gaskets seal around any inserted electrical cables to prevent infiltration into the inside environment. Captive fasteners include end portions integral with the box and can be rapidly tightened to secure the box to a stud or similar support. Thin tabs on the flanged vapor box provide a means for rapidly and accurately positioning and aligning the box against a stud or similar support. The alignment tabs are substantially thin to avoid creating a bulge in the drywall surrounding the box.