An endoscope overtube includes a flexible tubular member and a hub assembly provided at the proximal end of the tubular member. The hub assembly includes an elastic sleeve seal cuff extending about the inner surface of a body member of the hub. The ends of seal cuff are coupled to the body member. An inflation line extends into the body member in communication with the outer surface of the seal cuff. When fluid is pressurized through the inflation line, the cuff is distended inward to reduce the size of the opening through the port such that the cuff forms a seal about an endoscope received through the hub. The body member is preferably coupled to each of the flexible tubular member and to the elastic seal cuff using a snap-fit engagement of parts such that no fasteners, welds, glues, etc. are necessary for securing the hub assembly together.