I used a 4x4 across 4 trusses (on the roof's pitch to enable higher lifting height) for each of the two pulleys. If I was to do it again, I would use four pulleys collected into one central pulley. This would eliminate the strap stress on the cap, and the strap stress on the rafters when the cap is near the top. The strap stress is minor, but it is still there. Four straps would also eliminate the potential for the cap to "twist" between being lifted off the truck and before the straps contact the rafters. I would also use tie-down straps on the four corners to provide adjustability.
Right now, the cap clamps are removed using an air rachet (lazy), then each corner is lifted by hand and a block is placed between the bed and the cap. Next slide a 2x6 with eye bolts on each end under the front and rear of the cap. Then attach the tow strap ends to the eye bolts, center cross pieces are placed between the 2x6 to prevent them from sliding together when lifting, and finally use a come-a-long to raise the cap. The main thing I don't like about this setup is that letting the cap back down is a two handed operation using the come-a-long.