I use several Damp Rid units in my unit year round. I open all the closet doors where I can and have one in each room minimum. I would however if using the canisters place them in something as a failsafe to catch any water should they freeze, crack then thaw. The closet hangers I only use during the season since they are harder to failsafe with a pouch hanging in the air.
They go in my basment storage areas, bathrooms in the sink/or shower, kitchen area sink then bedrooms. I like the smaller units since you can dump and re-fill them as needed. The larger tubs have sawdust in them to absorb the water and are toss outs once full.
My vents are always open so I do get some added moist air but not a stagnant air that can do more harm than some moving moist air will.
p.s. on edit, I have Maxx air covers over all my vents which is why I can leave them open without worry. Do not do this unless you have covers.
2014 375 BHFS Eagle Premier
2014 Ram 3500 Longhorn DRW CC
6.7 CTD, Aisin, 4.10's