Thanks Waste. I hadn't considered the logistics of trying to put the bottom in on that depth, I should have thought of that, so that's a great point.

But, regarding "However, another alternative is to add an extra 4' wall panel to the sides (instead of having an 18X 36' pool you get an 18X 40' pool)", the object of this would be to make the pool longer or am I misunderstanding? My specs are hopefully are around 45 x 20 (or thereabouts). Thanks again for the help!