While I can see some advantages to this idea it was actually quite easy to judge when the wall was getting a bit thin as a distinct bluish light could be seen filtering thought the snow when the thickness was down to about 4 or 5 inches. I tended to repack a bit of loose snow back into such sections but I suspect there was actually sufficient wall thickness in most of these cases had I just left them as they were.
The total construction time was about two hours and as I had discovered a pre-existing fire circle close to the entrance I used a small fire tray between the stones and a couple of fire logs to boil up some water and fry up a bit of grub.
I had a synthetic sleeping bag with a home made Ventile cover for sleeping in but only a standard air/foam mat, never the less, I knew I could always retreat to the permanent sleeping arrangements in my van a short distance away if necessary.
It was quite predictably the mat which turned out to be the weak point in the system but this was sort of remedied with the addition of the folding foam mat from the back of my mountain pack. Serviceable but not exactly luxurious, it certainly firmed up my decision to invest in a Down mat before next year.
On the subject of lessons learned I would have to add that we should never under estimate the light levels and their impact upon our eyes in snow conditions.
About halfway through the construction I could feel my eyes becoming quite uncomfortable and I had to return to my stash of kit in the van for a pair of snow goggles. If asked I would have described the conditions as low cloud but had neglected to consider that the altitude I was at meant that the cloud layer was not actually very thick.
By morning the dome of the shelter had flattened out somewhat but it still afforded sufficient room to wriggle in and out of my sleeping arrangements. I suspect having the fire so close to the entrance affected the structures longevity to some extent but it did make for an interesting photograph.
Altogether a very instructive and valuable exercise, one I would highly recommend to anyone.