Garages, sheds and seasonal bins
The spaces nobody opens between long weekends, and what that does to the air inside.
Storage is the easiest win on this list, because storage is mostly small closed containers, and small closed containers are what a scent pouch is built for. A bin with the lid on is close to a perfect case.
So start with the bins rather than the room. Seasonal clothing, camping gear, holiday decorations, spare linens — one pouch per bin, dropped in on top before the lid goes on. Everything in there is dry and staying put, which is exactly the condition where three months means three months.
A garage is the hard case, and it is worth being realistic about why: it is large, it is drafty, the door opens twice a day and it shares air with outdoors. A single pouch in the middle of a garage does very little. Instead, treat the garage as a collection of smaller enclosed spaces and target those — the tool chest, the closed cabinets, the car itself, the bin of winter gear.
A shed is the opposite and does well. Small, closed, and rarely opened for weeks at a time. One pouch handles most sheds; two if you also have a closed cabinet or a bin in there.
One habit worth having: write the date on a bit of tape when you place a pouch in something you will not open for months. A bin you seal in October and open in April will have gone quiet long before you get back to it, and the tape tells you whether you are smelling nothing because it worked or nothing because it finished.