Yes, put a pinch of citric or boric acid in the wash out water, especially for the first 30 to 60 seconds.
Also, you do need to raise the humidity or humidify the paper after drying the sensitizer. Before I bought a humidifier i used to hold the dried paper over a small electric skillet with water just below boiling for several seconds until it became slightly limp. This increased my success rate tremendously. It also improved the D-max of cyanotypes and VDB's.
What does the humidity do? Increase the photoreactivity of the stuff?
Paul, I'd imagine it's much more arid here in the prairies (might as well be desert) than it is on the east coast, but I've never actually been there.
It's humid here in the summer, but it's exceptionally dry in the winter -- especially with the heating system in my building. I started doing my cyanotype printing during the winter when it was really dry in here and didn't have any particular difficulties.