why our thermal mass design has a gap between the barrel and the cob hat

I was just thinking as I watched this that this might be another huge benefit of the new shorty designs, you don't need the gap for any mass placed on top of the barrel. With the exhaust exiting horizontally from the riser, the temps will never get too hot on the steel. I love the look of the cob hat and the extra mass is great, but I like to keep the removable lids--though the only times I've removed the lid is to show people what the inside looks like and once to get an unfortunate bird out that had flown down the chimney and made it through 20+ feet of horizontal pipe to the barrel.

Great video as always.

Is there a more expansive discussion of what can be put on top of the barrel in a 'standard' RMH? I routinely put rocks and pots of water on my barrel to cook or store more heat once the yurt is toasted up.

In my case i warped the top (bottom) of the barrel when doing the original paint burn off, having left too much of the oil remainder in the can during the pocket rocket process. This makes for incomplete contact under a flat pot so maybe not a problem in my case (and if it did spall out it would be a good excuse to make a nicer replacement barrel). However, I've been telling clients that it is okay to use the center of the top to cook on or place water to boil and help with winter humidity.

What is the threshold for too much mass on the barrel to that could put the metal at risk?

(BTW, I would say that coming across little caveats and complications with RMHs like this at random is likely one of the reasons many more conservative homeowners look sideways at taking on the whole concept for installation. Would compiling these items into an easily referable list/manual be helpful to encouraging adoption?)