Freight levels drop for EVERY LTL company during the winter months, it's just part of the industry. What you fail to realize is that most of us sat at home at one point or another, it's one of the cons of being on the lower side of the road board. I, myself, sat at home during my first winter on the road board and that was before we used PT.
True, no one wants anybody to sit at home, but when the runs aren't there, the dock is always an option. They will let a full time driver pound the patio and ask a part timer to sit at home. Does any driver want to work the dock? No, but it's better than sitting at home.
If you're using sitting at home during the winter months as your argument for supporting the union, then that would've happened many moons ago. You also fail to realize that those same union companies that you endorse also use PT and they also have drivers who work the dock or sit at home during the winter months.
I don't like the use of PT any more than the next guy but the fact remains they're a necessary evil.