If I was to build my own WVO system, I would go two tank.
I would use a marine sytle tank for a Mercedes, metal one. I would put inside the tank a copper coil, with welded on fittings for coolant to flow thu.
Then I would run my coolant hoses down a flexible pipe such as a shop vac hose. Inside the hose would also be my fuel line.
At the tank also would be a racor 30 micron filter assy. And a small electric boost pump to help send colder veg oil to the filter in the eng compartment.
Once in the eng compartment I would run a filter such as this davco
http://www.davcotec.com/fp234.htm
And then to a iron tee fitting with a standard glowplug installed in it. Also on the way to the injection pump I would use a ford tank switching unit like in the older trucks. Just before the injection pump.
When I started the truck first thing in the morning I would wait five mins till the eng coolant was warm(not the tank) and then I would turn on the inline glowplug, and switch the fuel over to veg.
Oh ya and the shop vac stlye hose I would insulate in foam. First wrapped with tin tape.
Later the marine cruisday would be covered in hot water tank insulation.
This is an idea I had for a basic DIY veg kit.
I would not pay 800 for anything. Unless I was getting cool custom tanks and every darn thing needed.