Hi
just thought i would drop in on this thread,
I am also in the UK and have managed very well with a screen cage and have managed to keep the temp in a good range and my UV is a 5.0 and on the outside of the cage as is the heat bulb/dome. Never really come across any problems from friends or experts that i have spoken to about cold being a factor to using a wooden box instead of a screened cage!
Your cam looks good and have loved seeing the difference in pictures throughout your post

Just a thought but after reading the last couple of posts regarding sneezing, i believe that bacteria from stagnant water is a cause for RTI but also stagnant air which is a hazard caused by lack of ventilation.
Happy chaming