I used my QHY9 for the first 12 months with no sealing faceplate. I'd religously put the filterwheel and camera into separate ziplock bags with dessicant after each imaging session, then reassemble quickly before us. I've also been superstitious with bringing the camera to -1deg for at least 15-20mins before setting to -25. All this has worked well for me.
Went straight to -25 the other night and had a bit of frosting
QHY9 is pretty good with heater circuit around the main chip mind you.
I must try the argon one day though. Makes sense. Plenty at the lab, just have to figure out a way to get access to the plumbed lines.