My father-in-law worked home construction and repair type jobs all his life. He told me to never store anything, or hang anything from the trusses in a garage. They will hold ok, they can support the weight, but the roof will begin to sag over time.
For what you're proposing, if you don't want long term damage on your building, support the bottom of the trusses from the floor up, so the weight is on your (new) upright supports and not the roof itself. Then, you can hang a semi-truck from it without any affects to the structure.
You've got to remember, in homes with second floors, builders use floor joists (2x12's) or larger that can be walked on and are heavy enough to support a lot of weight. The trusses in your garage ar all 2x4, and they are no even a real 2x4 inches any more either!
Find a way to support from the floor, and you'd make my father-in-law very happy!
