I am frequently appalled at the lack of automotive respect for my tractor on the country roads. I have my SMV triangle, my four way flashers flashing and cars approach at high speed figuring they will be able to sail by when they get to me or get impatient (after 30 seconds) waiting for me to pull over, and pass in the most dangerous, blind places. When push comes to shove, it is going to be the tractor that gets sacrificed if a head on is imminent.
So what I do is crowd the center line making it less attractive to pass AND I swerve left and right erratically as if I'm about to make a turn and cars often back off. This works pretty well. I also pull over whenever possible.
What works for you?