I too have the HH Exp. and due to some limited mobility the bottom entry is about the only thing I can use. I was about to give up on the hammock idea when Rev told me about his experience with the HH bottom entry system. I am sold now.
My lowest temp so far in it has been about 40F +/-. What I used was a Wal Mart CCF (closed cell foam) pad (the 15.00 one as it is wider). I split the pad about 1/3 of the way from the bottom in order to allow me easy entry and used my 30F sleeping bag over me. Oh yes, I put a 2'x2' piece of Refective under my feet to keep them warm.
I had tried using my Therm A Rest in it but I spent more time chasing and adjusting it than sleeping. I even tried putting some of that non stick rubberized carpet underlayment under it and I still could not get it to "lay down".