Connect to the "panel points" on the trusses. They're the places where the bracing/bridging touches the bottom chord of the truss--where you see the punched metal "press plates"
I'd use a 2x6 against the sheetrock with a Tek screw into the bottom chord at the panel point of every truss it crosses.
A canopy shell weighs what, 200-300lbs at most? If you span 4 trusses on each side, you're looking at 50-75lbs per corner or 25-37lbs per truss. Go for it. I know of several people who hang their camper shells from the roof.
