[VAC] foam under black water tank

["Todd McDonald" <tod47d@xxxxxxxxxxx>]

While I'm at it.... The styrofoam under our black tank feels real 
heavy-maybe 10-20 lbs. !?! Possibly aborbed moisture over the years and I 
was wondering if an acceptable alternative would be the blue foam insulation 
sheets (around 3/4" thick) stacked up to similar thickness as the original 
styrofoam, or is the original supposed to be dense and heavy and I'm just 
imagining it to be overweight? again---- thankyou----tod47d