My preference is to either use the new compost when it is finished, or, if I need to store it, I store it in a pile on the ground, not too far from where I'll need it.
A dalek for storage is not a bad choice, at least it is ventilated. The only macronutrient you might lose in dalek storage is some nitrogen. Some forms of nitrogen are volatile, meaning they can escape as a gas (example: ammonia nitrogen).
Potassium and phosphorus will stay put.