By far the best set of directions I found comes from the i eat food blog. Instead of using an incubator or leaving it in the oven, though, I read "110 degrees" and thought, "Perfect!" then left in in a cooking pot outside on the back porch for some hours. The world is my incubator.
There were a few mishaps. Soymilk likes to sneak up and overboil like mad when you're not looking. Virtually my entire 2 L pot of soymilk disappeared over a 5 min period when I stepped out of the kitchen...I was puzzled that it could evaporate so quickly...but I later found the soymilk lake in the grease trap beneath the burners. Good thing I made too much soybean mush to begin with, so it was easy to make another batch of soymilk, but I watched it like a hawk the second time around.
I'm really happy. It's one of those open-up-the-black-box moments where I take something mysterious (yogurt) and figure out how it works. Like opening up an old TV set.