Hi Gordon. We did the same job on our 1991 Swift. It was just a matter of undoing the screws inside round the edge, pulling off the skylight, and picking off the very tacky, sticky sealant. Then make sure surface is clear of dirt dust and remaining sealant, apply new layer right round opening and firmly press new skylight into place. The sealant we used was the stuff on a roll, like very sticky blu-tac (sorry can't remember proper name).