No point in going looking for trouble, eh?
They used to use crushed volcanic rock on the roads here- we called it "cinders"- but the state switched to liquid de-icer a number of years ago. Accidents and cracked windshields went way down, but it's corrosive, so we have to regularly wash the undercarriage. I don't tow during winter storms, anyway.
I agree with Jimp. Towing on highways is unlikely to crack the plexiglass. All the rock chips on my
Scamp are below the belt.
I do get plenty of bugs above, though. My shield keeps the window bug-free. Over time you may also get fine scratches in the plexiglass from wind rash, as it's much softer than glass.