Sandwiched between the frame and the body is a plastic strip held in place by four of the bolts, leave these in place to hold the strip, (these are identified by the cutouts in the frame). Then run a thin blade or strong wire around the roof between the strip and frame. The seal between the plastic strip and body is a sticky back foam strip, a bit like window draught excluder, if possible it is best to leave the plastic strip on the vehicle as it is very brittle.