"THE VAULT" - Temp Cntrl - Heat & Cool???

How 'bout you build a small freestanding closet for your garage, use plenty of insulation and install a reefer on the outside with Johnson control for the inside temp? You can even put it on heavy duty casters to move it around when need be.
2x4 construction with OSB liner covered in Tyvek to fix an appropriate hard wood to and use spanish cedar for shelving.
The cabinet itself would be under 200$ and you can find a Vinotemp style external chiller for cooling which won't affect RH, and for the winter months a small but effective oil filled heater using the same temp control as the reefer.
Oh man I might just build one myself! A weekend project yay!