I need to carry one 20 ft lumber from HomeDepot to my home. I don't have a truck but have a minivan (Odyssey). The minivan does not have a roof rack though. A friend of mine suggested that I could open the window of the front passenger seat and place the lumber diagonally, making it stick out the window. But, I am not sure about the method and haven't found anybody other than my friend who suggested this method. The HomeDepot is very close to my home (about 5 minutes local driving).
If anybody has an experience of carrying long lumbers with a minivan, can you please share the tip?
EDIT: I attached the photo below. The first two beams are connected to the roof structure to support it. They are 18-feet 2x4. The third beam (shown in the bottom right corner of the picture) does not provide any support even though it looks so.