Like your Weber Silver, my Kamados are air-tight. I shut then down after cooking and probably 50% of my charcoal is saved for my next session. A bag of Kingsford will last me over a month, so I can spend my money on more important things...like bourbon.
Yep, my #7 Raspberry Kamado is not so air tight anymore. The Spider broke out of the collar, when the threaded rod froze. When I tried to help it along, the damper cap broke into two peices. It does store all my extra equipment well.