There are a lot of E series tank de-lamination issues out there. This is found on the Ford factory tank, not the aftermarket tanks. Check out www.thedieselstop.com in the van section. You should be able to find more info there.
I believe the older after market tanks also had the trouble. There was a large thread several years back on the SMB owners group that Tranfer Flow(?) had made some changes. Think it was Tony Stein that made the post but that was way back, possibly pre 2006.
You might check the archives there
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer