How should clothes and books be stored in an unconditioned space?
I can offer my suggestion for storing clothes and fabrics, but not books. 

When my wife and I had to store a TON of clothes, towels, sheets, jackets, sleeping bags, pillows...you get the idea....we used vacuum storage bags. 
Everything sat in a storage facility for over 2 years, the facility was unheated in the winter and zero air con in the summer.
Being in the northeastern united states the temperature band is pretty broad.
The VSB's worked awesome, no bag failed, everything came out clean and did not have a musty odor. 
The only issue was items were very wrinkled, but unless you plan of storing a wedding dress or items that you do not want smooshed, you should be fine.  

Other factors that we liked, easy to find items since the bags were clear.  Easy to stack and carry. The bags were really cheap in comparison to other alternatives.
They also provided basic water proofing, as the day we put it all into the storage facility it rained.