I don't think there is a problem if they are airtight contained.

I keep some of my overflow of fabrics & scraps in my garage and also check thru them from time to time and i haven't had any problem.....I live in Oregon so it's different weather then some but it gets very hot and cold in my garage also.
they are all stored in tote boxes except for one bunch i have in a laundry basket with a large towel covering the top.....one lady donated fabrics to me and they were very smelly being kept in cardboard boxes in her garage i think.
i used the vinegar solution in my machine to get rid of the odors....polyester knits I gave to Goodwill.....

I know that my suggestion may not be popular. When my stash outgrew my sewing room I forced myself to organize and get rid of what I knew I would never use. Donated many bags to friends who were teaching quilting at senior centers. I've even been invited to a show that one of the centers is planning to show off what they've made. Worked for me. Now I'm organized, can find what I need and can move around my sewing room.

If you were living in a humid climate such as that in the deep South, I wouldn't do it but since you are in the California Hills I think you do have options. As far as I know, heat and cold would not be your problems; mice and moisture would be your big issues.

You can keep fabric safe by using hard plastic tote bins with latching handles. I have noticed that non-latching lids can warp over time, allowing mice entry; that is why I recommend the latching bins. Here is a link to the type I mean:
http://www.walmart.com/ip/Homz-15.5-...-of-4/40977738
I also recommend getting the ones with the clear plastic tops; it's surprising how much the solid tops interfere with finding stuff later on.

Never store fabric in soft plastic bags. Aside from the fact that mice can easily chew through them, soft plastic "outgasses" chemicals that damage fabrics. Hard plastic does not outgas these chemicals.

Now that the mice have been taken care of, you absolutely must address the moisture issue. If insects are not a problem in your area, you can use a drill to make small holes in the plastic to allow moisture to evaporate. Personally, I would not do this. Instead, I would use dessicant pillows inside each box to absorb moisture. These are the little packets that you often find inside shoe boxes, vitamin pill bottles, etc. Save them and recycle them into your plastic totes. You can purchase these in quantity online, and you can also make your own using the granules used to dry flowers with. Here is a link to a place where you can purchase dessicant packets:
http://www.sorbentsystems.com/smallp...FUuRHwodOR8CBA
If you want to make your own, purchase silica gel at Walmart or JoAnn's (look in the plastic flower section of JoAnn's) and watch Youtube videos. Here is a link to one Youtube video that shows how to do it yourself:
https://www.youtube.com/watch?v=ly-o7sAsFtI

I'm in your position, I recently asked a couple of Walmart stores to keep the empty boards for me. I am in the process of putting my fabric on these boards, they are much easier to see and they take up less room. I placed mine on some shelving my husband bought for me. I am actually starting to see some improvement. My fabric and sewing machines were starting to drive me nuts, I'm now beginning to see great improvement. I have currently 40 boards full, and maybe 40 more to go. This is just the way I do it. Hope you get it worked out.

I had the same concern a few months ago and started this thread: http://www.quiltingboard.com/main-f1...c-t265779.html
I received a lot of good advice, but I think post #21 was the most helpful. I'm using her suggestion but with plastic totes and dessicant instead of bankers boxes. The totes I found are a bit larger than bankers boxes but not too much. Remember, whatever you use that fabric is very heavy.

I think instead of buying more fabric and trying to find a place to store it, I would start sewng and using what I have. I have to make myself stay out of fabric stores because I have a bad habit of buying just because I like it.

Fabric is stored in two goodwill china cabinets with glass doors. They are definitely not air tight. I found a long piece of fabric, also in goodwill, that had been stored with mothballs. The smell was not too strong, so I bought it.

I cut it into 4 large pieces and draped the lengths over the inside of the top of the glass doors. That effectively blocks sunlight (DH leaves the garage door open and sun beats into the garage) and, so far, rodents. The smell has not leached into the fabrics at all.

the smell is fading from exposure, but I'm hoping the bugs have stronger noses than I do and will continue to avoid my fabric.

Maybe it's time to buy a few mothballs and re-expose the door cover fabric for awhile.

I live in upstate NY...so get hot summers and freezing winters. I have an old fashioned wardrobe cabinet(the kind they used to use instead of closets)..in my garage...my overflow is on shelves inside the wardrobe, out in the garage. The garage does stay fairly cool, so nothing gets really hot, but in the winter it gets well below 0 out there...but it's just fine. I think humidity is the worst enemy of any fabric...if you live in a humid area..and insects..and rodents..but temps I don't see as the problem...fabric (cotton), needs what we need..air..low humidity, no rodents or insects. I am wondering if the people that had rotted out fabric after storage had high humidity before it was stored? Even those plastic tubs won't keep humidity out...that's why people that store food for future disasters use silicone caulk around the edges..to keep the humidity out..it's the humidity..not the temps..I think.

You can buy 100 comic book boards on ebay for 11 or 12 dollars, and they're acid free and meant for storage.