Hit or miss if you can make money
I think it depends on who you work for, what contracts they have and how busy they can keep you in off season. I worked two weeks for a guy and the trucks were junks, you worked your tail off and yet I was paid by the bushel and most grain elevators now limit your weight to stay legal.
If your paid hourly that is best because you can sit a while at some river points for delivery. Working for percentage is always tough if your faced with delays.
The other issue is wasted time because I was running grain about 70 miles to a ethanol plant, but then dead heading back to get another load. So half the time I was not making money. Frankly I can't figure out how this guy ever made much money doing grain hauling? Maybe that's why he had junk for trucks and never fixed anything.
As someone who was a owner operator for over 10 years, I can say for sure I would never haul grain to make a living. I think many drivers haul grain to avoid some of the trucking regulations. Heck I knew a few drivers who were never drug screened, did not have a CDL or a medical card. They probably ran grain to stay under the radar.
Then you have the farmer field pick up or a farmer bin pickup and you end up with no real ideal how heavy you are risking a portable scale or something. At least at elevators you know what your weight is before leaving. I finally decided the crappy trucks and cheap pay was not enough for the risks.
Maybe if you really need money and can find someone who has decent trucks and trailers it might be worthwhile at harvest time. But skip it the rest of the time unless someone is willing to pay hourly.