safety first!!!
I live on a farm, have tractors and implements and all sorts of heavy machinery- I do agree that a 150 litre tank filled with oil will probably weigh over 300lbs++. Welding is an option, as long as you go to someone with experience and know how. As a secondary precaution, I would have the tank clamped on with some type of metal clamping after it has been welded, just in case you hit a big bump along the road, and the tank somehow "breaks" off from the frame.
I use FARM DIESEL (Marked Diesel) for many of my diesel needs. If you go to a HUSKY Station you can get Marked Diesel for approximately 44.5cents a litre, but you are not permitted to use it with any vehicle that uses our highways or roads because you have not paid the ROAD TAX portion that is included in your reg diesel or gas.
What would be the legal issue of using veg. oil for a source of power? Would they bust you and say you are not paying for the upkeep of our highways and bi--ways???
I am very interested in alternative power sources, and still believe water is the best choice. You hear about fuel cells that contain hydrogen, bad idea. HYDROGEN ON DEMAND is the answer, and is presently being developed by these russian guys I met. (OLD SOVIET TECH) A small box the size of a package of cigarettes, contains + and - points where water would be separated ON DEMAND into hydrogen and oxygen. This would make your vehicle MUCH safer, than having 40lbs of hydrogen stored in your trunk. (Don't get rear ended!!!) This is the path I think we should take. The oil cartels on the other hand, would rather you not take this route.
Interesting endeavour though..... just go to Mc D's back door to fill up.... I am sure they would love to get rid of their used oil. On the other hand, They probably send it back to their distributor, where they clean it and then send it back as NEW CLEAN OIL for those FRITES!!!
Later.