If you are referring to a rigid roof, they are usually attached with sikaflex or tigerseal. If they are leaking you may have corrosion underneath and its better to pull of the loose stuff an properly prepare with rust eater and a good quality rust primer to save welding later.
If you are referring to a soft pop top such as the reimo roofs. It depends on the 'canvas material' the older cotton, nylon etc. ones can be sealed with silicone such as fabsil from grangers some newer canvases need a fluoropolymer sealant. Best ask the manufacturer of local agent.
tim, March 2010
