I haven't tried hammock bike camping yet but I sleep in a hammock full time at home and also have winter hammock camped. I've had nights in my backyard down below zero. I believe I was using a blue closed cell foam pad underneath me and I was sleeping in a synthetic 0 degree mummy bag. I did have plenty of clothing on as well. I've never tried using an underquilt but know guys talk about using them all the time. The biggest thing is to try out your system in the backyard before taking it on the road/trail.

I saw a post recently about guy talking about having a hard time staying warm using a 32 degree down bag with an air mattress. I spent the night out, about a week or so ago, in my backyard. I was testing out my new down bag I bought at Walmart. It was rated at 32 degrees. I saw 34 degrees and I was warm, even on the bottom. I was sleeping on a closed cell pad thought and not an air mattress. I think your smartest move when it starts to get cold is to ditch the air mattresses and go for something solid underneath you. If not you will probably need extra warmth underneath to insulate from the air in the air mattress.