I wish I'd have known a week ago, had a factory steel wall that I just drilled out and fed to my dumpster. I use console water tanks to keep the weight dist. as even as possible, so I toss them, 3 so far - sorry man.
I just bought another, I have a tech driving it in from NY as I type this, I have another in TX I am picking up next week, and will need one more. All are/will be the super tall models. If I end up with another, It's yours if you want to handle the shipping cost.
Also on the fuel tanks, I use marine grade inboard tanks, 12 gal. units from overtons. They provide for return lines (if EFI), you can buy vent kits, you can buy exterior fillers and mount it through a wall, etc. Lots of options.
I strap them down inside the van, vent them to the underside, fill from the inside, and I do have a ground strap. Some folks on the boards have raised issues with this, I'm comfy with them installed the way they are - I have had 4 vans set-up this way for about 6 years, one was in a pretty bad accident, zero issues. You just have to be smart about the fuel line type, how you route it, etc.
I haven't seen a universally DOT approved secondary tank for these vehicles, however there are a few non-approved out there, but they are not cheap, $1400-1500 pre installation - and where they locate them, a very minor accident could = a boooooom. I'd stick with what I had even if those tanks were the same price as the marines I use.
http://sprinterstore.com/specialty_parts.htm
Heres a post with some pics of one of my older sprinters
http://mikeysboard.com/forum/viewtopic.php?f=1&t=28230
