i got foamboard under neath my hot tub, to keep the sound down
(the pump used to vibrate a little, more like a humm, that i could hear downstairs)
i think that an the concrete flooring will protect the bottom
my real question would be...how does the outside hold up to the freezing cold?
and that brings up something else
imagine you're a rodent and your outside in the freezing Oregon winter
so what do you look for?
a nice warm place where you burrow into and survive the winter
now picture a plastic tub full of 102 degrees hot water sitting on a soft little foundation of chewable foam
i think that may be a serious threat to your longevity there
