Upon removing drywall in our 1920's house we came upon two airs ducts, one for hot air and the other for cold air return. We think the ducts have asbestos paper layered over the them. Nothing has been disturbed, and we're re-drywalling but we'd like to seal or cover the ducts before the drywall. Some have suggested a vapour barrier and/or some sort of spray sealant. Has anyone encountered this situation?