I have made a comparison between different storage methods. I can maybe post specific report later, but I can tell you quickly that;
The preferred method is to use PET soda bottles and squeeze all the air out of them.
Refrigerating chemicals (even without any squeezing or butane) is surprisingly very good, as good as squeezing all the air out.
Butane works but is not as efficient at all as the above mentioned ways (squeezing air, refrigerating)
If you use butane, you have to use large amounts of it. "Butane is heavier than air and forms a layer between air and solution" is not true. You have to displace as much air as possible to get the desired result.
Thanks. I was planning on using soda bottles for mixed chems, but not the concentrates (due to the low volume). Is it safe to refrigerate the concentrates?
Yes, it's safe to refrigerate. Freezing may not be wise.
If you cannot squeeze the bottles, add butane (if you have it) AND refrigerate. I would guesstimate they will live for more than a year this way.