Send it to me. I'll take it to the bottom of the sea
But really store it in a place where there's
- a low chance of big temperature fluctuations
- Near room temp (60F-80F)
- Away from chemicals or car fumes
- Away from cats
- Make sure all gear is bone dry
- Keeping the area ventilated isn't too harmful either (ie. a closet that opens daily)
Some samples are your house closet, game garage, in a rubbermaid box etc
Depending where I live, sometimes I'll put my stuff in an 24gal Action Packer and leave it in the car garage all sealed up and dry. My BC and wetsuit however go in my closet. My regulator and computer are in bags of their own, which are then placed inside the Action Packer.
As long as you aren't running your car in the garage or trapping chemical fumes it should be alright for your gear to be sealed up in the same area. Provided you follow the above guidelines.
If your garage gets cold and damp in the mornings then it's probably not the best place for gear storage.