So, my plans of originally playing a badass necromancer has been replaced by completely owning everything as an Arcane Hierophant(Druid4/Wiz1 with precocious apprentice that will get retrained). As a necromancer I was planning on creating an "airship" per say, and by airship I mean "A castle or fort on the back of an undead dragon". This plan will no longer go as Druids hate undead and my DM is one of those guys who love fluff(was able to get spellstiched through my background), but I still want a really unique airship. The DM promised me we will get an airship and he'll work with me to get whatever I want(he would have gave me a colossal+ pyroclastic dragon corpse). So my thoughts are "I should put our base on an animal now" and there is where I need help. Could anyone suggest a big ass creature we could put a fort/castle on? I know I could slap the titanic creature template on something, but I thought you guys could give me the most optimized suggestion.
All books are cool(3.0/3.5/3rd party/Dragon)