HH makes an under pad for theirs. I have used it, but never in the colder months. The warmer months arent an issue. I plan on trying out just a normal CCF pad this spring, and see how comfy it is.
As for the HH itself; this is a great product. A lot of people get these, then move on to other hammocks, mostly made by small manufacturers. But, with an HH, you can NOT go wrong. I also have a DD hammock, which is used soley in my jeep; its not near as comfortable, and I cannot seem to sleep flat on it. But, in a pinch, it beat sleeping on the ground. The HH however I sleep flat in, no need for a pillow even. The tarp it came with originally has been replaced, and I had some modifications done to it (mainly, had a zipper installed on one side, to make it a side entry system), but, these are asthetics only. I never had an issue with rain with the original fly; I just liked having additional room to cook, and to keep gear dry.