I just started doing customs and Mr Super Clear UV is good to use. I live in Australia and we're a few weeks off winter now and what I can say is it's good so far. No smudging, no running and no problems even for a beginner!
As for temperature stuff, the fumes from this product are bad (I gave myself a nasty headache yesterday from it so beware), so spray outside and bring it indoors. It shouldn't hurt it as it can continue to dry from there. It's the spraying part that you need to avoid breathing in but once it's on the doll it should be fine from there, just keep your distance as a precaution. Hope this helps even just a little. ;)
Another question, do I have to buy myself a respirator mask type thing or is there something simpler and cheaper I can buy to protect myself from the fumes?
As I said I'm really new to this stuff so I have too many questions
Gloves and a mask would do well to protect you, maybe even safety glasses too so it doesn't get in your eyes if you're that worried about it. ;)
If you can't get them, find a nice place where the breeze isn't going to blow the spray back at you, so a nice open area is a must (but make sure you don't do it around any pets or animals! Forgot to mention this previously). Like I said once it's on the doll it's more or less fine to bring indoors but I would wait a minute or two before bringing it in just to air it out so it won't be too smelly. Nights, evenings and/or mornings would be more suitable for spraying as it's hopefully more or less cooler during those times. I've been doing mine evenings and nights without issue thankfully. Best of luck, I can only speak from what little experience I've got so far. :)