This is what I do. Plastic bags and WD work great. I made some toe plates with some scrap 1x6s. I also cut a piece of hardwood that lands on the edge of the wheel so I have a nice repeatable place to put the level. I also marked the ground with tape showing 20 degrees both ways since the steering angle is more than 20 degrees. If you really want to be precise, the multiplication factor is actually 1.42 for 40 degrees total sweep, not 1.5.