I speculate what might happen 10 years from now when you need to contact STMPO about a warranty claim should something happen to one of their tanks, who's to say they will or won't be around to guarantee it at that time..
Just asking, but how does STMPO warranty something when Ross now refuses to even speak with us? I love Ross, but his hot headed attitude towards the NSX crowd caused him to alienate himself and now we can't even purchase his awesome goods. How the hell are you going to get a warranty on something you can't buy?
Some folks choose to do things the easy way, others the hard way.
This design (regardless of material thickness) is the same as the tanks that cracked... the weld will fail not the material... it is for sale though and the others are not.
The pdf included explains why there is a life time guarantee that is currently being speculated on... In my opinion - It also outlines what "the hard way" would be