I took the lid off my heat battery a week or so ago to check things out. The styrofoam board insulation had melted away to almost nothing on top and partially on the sides. I topped up the sand again as it had settled some more mostly due to the disappearing styrofoam. Remember that 1/4" concrete board that I used for a heat barrier around my wood stove when it was in the old mobile home? I cut it up and fitted it onto the top of the sand. Then I laid R12 pink insulation on top of that and then put the plywood top back on. The heat battery retains heat extremely well. I can get by with one good fire a day in most cases this time of year. If you let the fire go out it will continue to convect heat up into the coach for 3 days or more afterwards! I have also been busy setting up a few surveillance cameras on the property so I can keep an eye on things/weather when I am not around. It was a very mild winter here this year---the complete opposite of what I had last year.