I use a home made eyepiece heater (photo attached) which plugs into my home made dew heater controller
. Mike has another little DIY article about making these... only costs couple of bucks if you can solder. This keeps the dew off the eyepiece in use. The eyepieces in the tray I keep the top cover on until they are used (just rotate them around) and keep the lid of me EP box shut to keep the dew off those I'm not using.
I haven't been sorely tested since I've had the EP heater, but if my EPs fog up even with the top caps on, I'll use the 12V hairdrier to zap 'em.
Hope this helps.
Al.