I heard that water freezes UP not OUT. Does this make the pillow unnecessary for me under my winter cover here in Colorado? I probably need a new liner and now's the time to figure this out. I haven't noticed bowing from the past 4 winters. What I HAVE noticed is liner damage/wrinkling on the sides from the water level going down too much from (I'm guessing) evaporation over our dry winters. We didn't have that problem so much when the cover was new and waterproof, but he past two years it has vented itself from wearing in places. Thoughts?