I also noticed the inside of the objective lens was a bit foggy so I brought the whole system in, seperated the scope from the filter wheel and from the camera and dried them all out in the boiler cupboard (drastric measures !).
I have now reassembled and returned them to the observatory and ordered a usb dew heater strap for the objective, coming later today. If needed I will order another one to sit as close as I can get it to the filter wheel. Then when we get a night without cloud in what’s left of 2020 I will try it all again.
I have seen an option where you can take off the imaging camera and add a “dew cap” to the end of the scope and inside sits a dessicant pouch. This should keep the filters and inside of the OTA dry. The problem with this is you have to take off the camera each time and it spoils any setup (orientation and focus) I have achieved. Also it only works until you start imaging and as I have experienced, dew can form in the first hour of observing.