Okay, I got to test it for one hour.

When I started the temp of the thermometer sitting on the top of the sleeping bag was 39º

I lit 6 candles and left them uncovered for 15 minutes and the temp reading was 44º.

At 30 minutes it was 48º. At that point I put rocks over the candles and the thermometer in between the bag and the neoair pad.

At 45 minutes the temp was 50º in between the bag and pad and the tops of the rocks were still cool.

At 1 hour the temp was still 50º and the tops of the rocks were just warm, but not hot. At that point I snuffed the candles and set the thermometer outside for 5 minutes after which it read 35º.

The short of it is, it worked pretty good. I need to test it out with just the candles for one hour, and just the rocks for one hour, and then see how long the heat from the rocks keeps the bag warmer.

I'll post some photos of how I set it up tomorrow.