I know this is old but I had the same issue in my trailer. The knob stripped out.
So after reading and being frustrated I ended up at Camping World today. I took a knob out of a new Vortex and wandered over to the window/hardware section.
I grabbed a white, round, replacement knob for the side crank out windows with a 1" shaft, NOT the 1/2" shaft. I compared the splines and they looked the same.
Upon getting home and testing it, it appeare it would work fine, but I also remembered the vent being a tad rough or hard to crank open so I went ahead and pulled the entire Vortex back out to inspect. Once I got to looking, the little plastic gear drive adapter that moves the handle closer to the edge (away from the center) was semi tough to turn.
I took it apart to find all plastic on plastic with no lubricant, bushings, etc. Nothing was damaged at all as this Vortex is less than two years old, just everything dry and tough to move.
I grabbed some Lucas wheel bearing grease and coated every surface, gear, face, etc and put the unit back together and it works ten times better than new, and "should" reduce the chance of stripping my replacement knob/handle. Graphite might be a better choice, but I didn't have any! :-)
Here is the knob I used. The screw that comes with it "looks" too long but its not, it worked just fine.
http://www.campingworld.com/shopping/item/white-window-knob-1-shaft/36119
Enitre repair was probably 20 minutes and only a phillips screwdriver and some grease is needed.
Hope this helps!
Greg