An enclosure (10) for machinery or other items comprises a base (12), opposed sidewalls (38,40), opposed endwalls (20,22) and a top cover (42). The endwalls (20,22) are fixed to the base and have side edges (28,30) which taper inwardly toward one another from bottom (26) to top (24) and are bent inwardly to form flanges which mount a strip of rubber (32). The sidewalls (38,40) extend between the side edges (28,30) of the endwalls and rest against the rubber strips and the base. The top cover (42) is formed with a pair of opposed side flanges (46,48) each having a strip of rubber (54) mounted to the inner face thereof. Preferably, the distance between the rubber strips (54) on the opposed side flanges (46,48) of the top cover is less than the distance between the sidewalls (38,40). The sidewalls are mounted to the endwalls by deflecting the side flanges of the top cover outwardly relative to one another, moving the top cover downwardly to a seated position against the top of the endwalls and then releasing the side flanges of the top cover so that they deflect inwardly and their rubber strips engage the sidewalls to lock them in place against the endwalls.