I bought the Triumph cover made for the bike. Seeing that you are under a carport, the light cover will work fine and costs about 100. It is designed to fit America/Speedmasters with or w/o windshield and with or w/o backrest. It also is wide enough in the back for saddlebags. It has velcro tabs to take up the slack if you don't have a windshield or backrest.
Another plus - it can compress to a very small size and you can take it on the road. I always travel with mine as you never know when you might have to park near a lot of dust or under pollen laden trees.
