I have never seen dew on my optics in my Sirius 2.3m dome.
I have a dew heater pad behind my Newt secondary and around the inside of the OTA just in front of the primary mirror and here in Canberra, during the late spring, summer and early autumn I don't need to run the dew heaters at all but I do keep the three rear fans running all the time and they suck air out of the back of the scope. In winter, I also keep the rear fans running and generally run the tube heater and put the secondary heater on a low setting.
Canberra is of course known for it's generally dryer climate.
In warmer coastal and humid Newcastle I didn't have any protection and with the secondary and tube heaters running and the rear fans sucking, I
never had dew on my optics.
Mike