I think natural Ultra Violet “Sun” is a must for many arboreals to be healthy. I set up an indoor-outdoor enclosure for Bolins in Denver Colorado some 14 years ago and within a year the female became gravid. The difference in a snake that has gone from no U.V. or a snake that gets a florescent bulb to natural sun is amazing. The vigor comes back they become a much different animal. Here is a before and after shot of a Uncolor Cribo that has had natural sun for 2 months. Top pic is with florescent bulb and bottom pic is him with natural sun. There is no way that reptasun can compete with the real thing. Real sun also stimulates breeding see very bottom pic.
I live in Kansas USA. The foam plug keeps the weather out and the snake can sneak out on nice days. We have minus 15F degree days in winter here. I think you have a milder winter. On a 70F day a black snake in direct sun can get 90+ Degrees. Here are some shots before the spray foam.