I tried the stock Deep Jungle XL with the reflector pad on a windy and snowy 0 degree night (32F). I had to bail around 2AM when it became pretty uncomfortable on the underside.
I could have added my jacket, clothes, etc. under me, but I was interested in finding out my personal limits with the reflector pad.
Thought: Much in the same way you want to use a foam mat under an air mattress in freezing temperatures, a thin foam pad under the reflector pad would probably do wonders. At 2am, with the wind blowing under my hammock, the air-filled reflector pad felt more like a heat sink than a heat reflector.
I will have to try the thin foam cover one day soon.
It also shows the importance of test hanging where you have a warm place to bail out. I may have been able to tough it out, but simply surviving the night does not constitute a successful hang in my books.