To repel fabric eating moths, do I need to cover every wall, floor and ceiling with cedar ?

Nope. You just need airtight. Note item (g) under Management: http://entomology.cornell.edu/cals/entomology/exte... and http://www.ent.orst.edu/urban/clothes_moth.html:

"And finally, cedar oils, at concentrations present in most cedar chests, have almost no value as moth repellents. The value of a cedar chest is in the fact that the chest is tightly closed, thus preventing exposure to moths or beetles. So enjoy the aroma of your cedar chest but don't expect it to chase away any bugs!"