Climate-controlled ideal, shoebox-scale acceptable. No room? Clean a closet.
Cardboard boxes absorb humidity. Heat warps plastic shrinkwrap and degrades tape adhesives. Direct sunlight fades box art. The condition of the box at exit determines 20-40% of the realized value. Storage isn't optional — it's an operating cost.
An investor with a beautifully-curated portfolio and a damp basement will underperform an investor with mediocre picks stored in a climate-controlled spare bedroom. Storage is leverage. Better storage = higher exit grades = bigger ROI.