Go to a truck stop or truck and trailer place and get Truck-Lite part number 9021 (red) and 9021W (clear). This is a kit that has the lens, foam gasket and new screws.
Some butyl between the can and housing is a good idea. If you use a sealant, you'll never get the can out again without ruining the can.
Work is never done, so take time to play!