Friend of mine and I share barrels of C-16. My wife absolutely refuses to have it at our house due to 3 cars in the garage (space limitations). We also just had a new baby and she doesn't want to worry about bombs going off if you know what I mean.
My friend made a rolling stand that the barrels can fit on with wheels on it. He has a detached garage and his hot water heater is NOT in the garage, which is nice. The only recommendation I could make if you are going to keep it in the garage with a hot water heater around is to bleed the barrel every week or so.
Meaning...crack it open and release the pressure, then seal it back again. Also what HUA said is correct. If you store it outside, make sure its covered and out of direct sunlight. If you have landscapers....make sure they know not to stand around it and smoke or whatever - LOL. Some of this is very common sense, but you would be surprised how stupid people can be sometimes.
Shane