Many years ago a lawn irrigation specialist recommended I use thermal cover in addition to winterizing my PVB (24" above ground). I think the name of the product was "Polar" something. It worked for many years in my old house -- never had a PVB froze yet. However, in my new house I installed a new PVB last year and it just cracked yesterday over a two week period where the weather got frozen again. I have two questions: 1. Anyone know the thermal cover I'm speaking of? It's green and looks like a pillow but open on one end so you can slip it over a PVB assy. 2. What's high quality PVB (3/4" opening). Thanks.