Windshield constantly freezeing over.

I have tiny window seal leak, too.

As for your windshield freezing, I would tend blame the defroster.

So let's secretly switch everyone's regular coffee brand to Folgers and listen in for comments.

 

If you have an clutter on the dash that does impede the defroster’s ability to keep the windshield warm.

 

This happens to me when it’s around 0 and there is fog out.

I usually just keep driving and look through the tiny 4”x4” peep hole where my defroster is blowing - everything else is solid ice ....

 

Heat on high (like sweating hot), wipers going constantly, and when ice starts building up give good a sqirt of washer fluid... Also pull your visors down so they are about 4 inches from the windshield.

 

I had this condition a few weeks ago. Sometimes Mother Nature dishes out more than the truck engineers can handle.
I found the best solution in my instance was to slow down to about 45 mph, then the amount of mist hitting the windshield came down at a rate the defroster could handle.
Yes, put controls on maximum heat, the defrost engages the ac compressor on purpose, it helps to dry out the air. If with heat on full it still feels like cool air, then the blend doors in the HVAC unit are malfunctioning.

 

this. x100

 

Western Star's are really bad for windows fogging up. You have the defrost on, the side windows fog up. Switch it over to vent air with the vents pointed at the side windows, and the windshield fogs up.

The best solution I've found is keep the visor down like others said, and set the defrost to high, and crack the passenger side window a bit. Helps circulate the air a bit.

 

Fill your washer reservoir with RV antifreeze and use it liberally.