I put one of these on my windshield and we don't have any of the problems the have been described in this post, with a trailer or without.
MRA 4025066125036 X-Creen Clear Bolt-On/Add-On Variable Windscreen Spoiler Blade. If you don't want to drill mounting holes in the windshield, order the optional clamp-on adaptor at the same time. The spoiler blade is adjustable for height and angle. I'm 6'6" and a look between the top of the windshield and the bottom of the spoiler and have much better visibility in the rain than trying to see thru the wet windshield. You'll probably need to lower the windshield to your eye height. Also, I usually keep the helmet visor up about 1/2 way and get very little wind in my face thru the gap. I highly recommend this Spoiler. I'll never ride a motorcycle or Spyder without it.