Don't store the best things you got in the warehouse, couse evry supporter,capitain,kingpin and master cen take it! Yust put some MP,FP or HP pots or some other usefull stuff on it if you dont need them. Evryone (that cen)may take evrything from the guild warehouse, but if you don't need it ,don't take it.
You can also support on the warehouse. Yust klick Support when your in the warehouse and then you can fill in how much money you want to support in the bar 'contributin' and qeust items (QI) in the box above the 'contibutin'(by draging it in the box) . if you klick on 'trophy contrbution' then all you QI(from you inventory) will come in the box.
Thats called supporting. I can see in the member list if you supported and then i'll give you the title of supporter.