I wondered if the climate or weather would hurt the dept. issued cylinder or regulator that I leave in my Unimed bag in the SUV. Air Gas East, pretty much the only EMS oxygen people that I could find in the state, said "Depends". It depends on the normal climates, etc. If you live in an enviroment with "extreme" climate, i.e. Alaska, Northern Canada; Arizona, Texas, Mexico, etc. High temps could ruin the seals and O rings; low temps can break the diaphram in your regulator. But with a shifting climate, no extreme changes like real cold to very warm in a matter of hours, such as Pennsylvania has, it shouldn't hurt it. However, for safety sake, All "Chemetron Cylinders, if possible, should not be left in temperatures that exceed 110*F, or drop below 38*F, for an extended period of time. The same goes for B&F, Flotec and Hudson Medical Gas Regulators".
So. I just bring the bag inside when its cold. Not really that heavy, so if I need it, I bring it along. If I don't have it with me, I go to the fire house, no big deal. But its a better plan than having to replace the brass and rubber O ring, which are more expensive than the plastic (vinyl) green rings, but last longer and comply with federal standards. (according to the oxygen people).