http://www.vwvagabonds.com/
A very nice couple who sold it all and traveled around Central/South America, Africa in a VW bus, non-veggie but they wrote a great book, have a website and live in Cali..email them.
http://biodiesel.infopop.cc/eve/forums/a/tpc/f/159605551/m/936602174
This guy drove from oakland to argentina on mostly veggie.
This is from the forum I linked to earlier...you need to spead alot of time in this forum learing if you are serious about the dual fuel concept.
I love the veggie concept but it is a hobby unto itself with many issues...then concept of pulling up to Mcdonalds and topping off the tank is very far from the reality. Filtering will be your major issue and one you need to spead serious time looking at. Also realize that while much of your trip will be in warm areas where tank heaters and inline heaters aren't as important you will cross some serious mountains that will tax your system.
Also realize you will have too look for oil along the way....there isn't as much fast-food asian resturants (best oil) in central & SA and oil gets used hard....not to mention you are looking for only veggie oil not animal....again lots of research needed.
I would highly recommmed a 94-98 Dodge 12v CUmmins 3/4 ton 4x4 with manual trans, putting a camper shell on it and setting up a mobile centrifudge filter system where you keep the original diesel tank full as backup, then add another under bed tank for veggie, then in the bed you have a dirty oil collection tank (use a vacum draw setup with hose, easy to research) then comes the current debate...heat & settle in this tank overnight & then centrifuge or just loop the centrifuge while driving until oil seems clean (use clear hoses) and then turn a valve sending clean oil to clean tank underbed or in bed.
You will also want a backup system like filter bags and a heating element in case of primary system failure.
Finding oil will be the big issue....you want the ability to get alot if you can find it...you will need good spanish skills and might offer to pay a bit...you will be explaining your rig many many times.
I know there are some groups helping to set up WVO & SVO (waste & straight veggie oil) projects in latin america...google them and email for advice on getting oil.
Of course we haven't touched on if you will be camping/sleeping in the rig or hotels more. Mods to the rig to run veggie (no rubber hoses, keep it to simple 3 way brass valves vs elect valves....heating setups...recovery gear, your level of experience in offroad or other country travel, can anyone speak spanish......lots of questions
Tell us more so we can tell you more....also read read read....there is usually someone who has tried whatever you are thinking of before out there...
enjoy
1leglance