Yes, the Adventurer's Inn "trick" is the only safe way of storing your items in MM8! You have no base in this game. The chests in the Tradehouse will reset with Ravenshore regularly!

Nevertheless, don't give up the rest of available chests. Most of areas reset once in 2 years so that you can store your items safely in these chests in between. My "base" is always the Chapel of Eep in Ravenshore: it contains 12 chests and I have the inn at hand. Ravenshore (and the Chapel) resets once per 2 years. Thus, I occupy the chests and if the 2 year's limit approaches, I move my property to the inn.