Well this winter here it hit -55C (-48F) but at least we have a good gas furnace and half decent insulation. The living room did hit 67-68F but I didn't realize that the heating duct for the room was disconnected! I hooked it up now and we just had a -8 night this week. The room was still decent so a space heater will give me the boost I need if I have to next winter.
I was thinking of adding a second strip if heat tape but I think things will work out as is. Time will tell. My main concern was holding enough ambient temps and it is working well right now. I won't get the 85f ambient I here some breeders like to keep. I am happy with 77-80. That is at the extreme cool end. It gets better a couple inches in. Then 80 is held throughout.