Can anyone suggest a suitable underlay for an engineered wood floor? I want to use the Tongue-Tite system or secret nails and there must be a damp proof membrane (even though I've recently concreted etc. the sub floor crawl space to try and eliminate humidity). Problem is nails etc. puncture the membrane so lets the damp through. I've been told of an underlay which seals the nail perforations, anyone else heard of this?