If you dont have any sources for oil, don't even consider it. It doesn't just fall out of trees anymore. Start searching now for spring. Not only do you have to convert the bus, you need all the details worked out about gathering oil-storing it-cleaning it-etc. Greasing isn't for the weak of heart.
Although the forum isn't as active anymore, if you scan the archives at www.greasecar.com
there is tons of great info.