Build your own AH on your own guild island and list your items for 1 silver u have no limit on storage ( cost a bit silver but who cares when u have so much materials).just put in a buy order how much u want out from your private AH then u dont need to buy for those 2-3 mil guild chest slots
I am a trader. I would rather turn things over than to hoard them. So, rather than paying a storage fee, I would be getting a profit for every stack. I noticed they don't manipulate food prices. Trading food related could have lower requirement for warehousing.