An airtight enclosure comprising a pair of enclosure shells each having a pair of first edges and a pair of second edges extending transversely to the first direction. The first edges are spaced apart by a distance corresponding to the length of the second edges, the second edges are spaced apart by a distance corresponding to the length of the first edges, and the first edges have complementary assemblages for assembling first edges of the enclosure shells, and at least one of the second edges has a groove for accommodating a resilient sealing member in sealing contact with a second edge of the other one of the enclosure shells so that mating edges of each pair of second edge portions allow being assembled within a range of relative positions transverse to their longitudinal direction with the resilient seal or gasket in sealing contact with the mating edges.