Since you can't get into HGM or even West Cave until level 150 I think a pretty simple quest of sorts to make some key storage would be easy enough. Have some monk or the witch's sister or whoever make up some story about discovering a magical storage for all their keys. They need 5 mithril ingots, 5 soul stones, and 5 magic trunks or something because... you know, magic...
Maybe the tavern owner cuts off your beer finally and tells you he can store keys as well.