Wine cellar dilemma

[Kcwhippet]

We have the same situation (sort of) in that we have 2 walls underground and a bunch of insulation for the rest. Size is about half. We get pretty much the same temp ranges. This passive cellar has been in place for about 25 years and we have about 800 bottles - some dating back to the late 80's. We haven't seen any problems in all that time, so I believe you may be overthinking the situation. My thoughts are you should be fine. BTW, I've been doing wine since the early 70's and have been ITB for over 20 years.