Thanks for the replies so far:
Lefty - for the resistor suggestion
Bobnova – solar panel(s) are self draining (pumping the pond water through it so antifreeze not an option if I want the fish to survive), and water pump will be turned off before internal panel temperature reaches freezing.
Drmn4ea – your experiences are illuminating, and I had not considered condensation. The fact I am considering future wireless control, from your experience keeping the module warm will be a consideration.
Techone - I know the pink stuff very well, used many sheets on my train layout for scenery the new purple has better R factor, as for rain, Calgary is almost a desert re: rainfall, and the snow is dry ;^)