I am installing floating laminate flooring on a ground floor over radiant heat. Here is the construction: Concrete slab (part new, part 40+ years old), 3/4 plywood and Upnor Quicktrak. Question is, what type of underlayment and do I need a vapor barrier? I've used cork before and really liked how it performed though it's not cheap. Can I use the cheap foam most manufactuerers offer or should I 'upgrade'? Thanks