I'm still waiting for a permit, so I'm fine-tuning and estimating the finishing touches for an Intex 18'x48" AGP. I'm pretty much sold on the insulation-underlayment concept but scared by the prices. Yikes! If I go with the pink stuff I'm leaning toward 3/4" T&G with a 25 p.s.i. for $12.28/4'x8' sheet at Menards. They also have a 1/2" fiberboard "weather resistant" product for $8.99. Is that even worth consideration?