Oh no.. I'm happy with my current tank. No plans for more. I haven't actually done this, using the PVC sheets... but it sounded like a good idea so I checked into it with Sanitred to see if it was feasible, which they say it is. My tank is just all Sanitred. I like the idea of a solid rigid shell making up the bulk of the tank though... if I was make the tank today this is probably what I would try. But I would test the PVC to Sanitred adhesion myself probably. It takes around 14 days for bonds to cure even though you can walk on the stuff after an hour. That's key if you're doing a bonding test.
I think the PVC sheet idea would be a lot less expensive too. I probably have about 4 X the suggested coating on the tank... this was part of the effort to get it to stop leaking. So all these product manufacturer suggested use is just what is possible, but from experience it usually takes a lot more to be successful. And the bigger the tank, the more chance of failure, so the more likely that you'll be putting down more arbitrary layers to succeed.
If you followed Nolapete's thread, I'm confident that this was his issue as I pretty much dealt with the same problem. If he just kept layering sealant he would have got it eventually. He was probably one more layer away from having his tank going. Plus, he had it not leaking at about the 5 foot mark. He could have just went with that and put a spacer at the top of his window to hide the gap and would have still had one of the biggest tanks around. But I guess it was all or nothing for him.
Speaking of the stacked lumber method and Nolapete.. does anybody keep in touch with him? I'm just wondering what ever happened to his 4300 gallon tank.