Following this with real interest!
Blimey that formula is really hard to follow, but I've just about done it for my tanks, purely as a maths exercise and to compare that with the preformed ones on the website whose link you gave on my thread by the same name as yours.
I've made a spreadsheet on excel to help as I was getting a bit flummoxed with what was what, but I got there in the end!
What is the foam ppi and thickness are you using there?
Would you mind giving the rough costs so I can compare it with the preformed ones?