hello,
I have an 1983 300sd... I drove 348 miles this week on straight veggie oil... that i got from 1 bar and 1 grocrery. I filter it with the leg of a pair of blue jeans that i get from good will and I pour it straight into the fuel tank... I have no second tank....

If your dieing to have a 2 tank system... go buy an old out board boat tank... or 2 of them... and strap them down... I have seen them for 10 and 15 bucks... and they are usually 6 gals.... I think the cubbies might not be very safe...

as far as filtering oil... you really dont have to filter it at all....All the nasties and uglies fall to the bottom.... So if you take a bucket and let it sit all the bad stuff goes to the bottom even water... so the stuff you skimm off the top is clean....let your oil sit a few days... then take the stuff off the top.. and pour it through a filter bag or leg of a pair of blue jeans... then go ahead and drive on that.... I pour mine in a glass last night and eyeballed it and it looks very clear.... clearer than diesel...