For those interested here are some parts I ordered to add extra fuel filtration to my sprinter. Obviously these are part of a custom install. It is fully reversible. Other than re-routing the feed line before the OE filter, the stock system is untouched.
Here is the head assembly for the spin on filters. 1"-14 filter thread, and 1/2"NPT inlet/outlet ports.
P562261 $18
https://dynamic.donaldson.com/WebStore/search/item_detail.html?item=257965
Here is the primary filter and water separator. 10 Micron, Synthetic media, 120GPH, has drain. 95% emulsified water removal.
P551001 $16
https://dynamic.donaldson.com/WebStore/search/item_detail.html?item=417346
This the 3 micron secondary filter. Cellulose media, 120GPH. No drain.
P551313 $11
https://dynamic.donaldson.com/WebStore/search/item_detail.html?item=193205
Also needed for the T1N, 3/8 Fuel hose, clamps, 1/2"NPT-> hose barb fittings.
The total should be around $100-120 for materials. Obviously mounting and whatnot could be difficult depending on individual skill level. Note that all of these filters without the clear filter bowl are rated to 100PSI. So they are safe to use on the pressure side of sprinters with the OM647 engine.
Edit: I got my filters from here. You need to know the part number to order.
http://www.filtermaxx.com/
Edit 2: Here's a photo of the setup (not installed yet).