Update:
Uploaded a new ESP file that adds a couple of Furnishings to the sanctuary.
-Enchanting Table
-Alchemy Table
-2 Dagger Display Racks
-A Satchel
-Strong box
-2 Weapon Racks
-Unique Dragon Priest Dagger with Fiery Souls enchantment. Temperable.

Edit: Forgot to mention that the Mask brings you back to the last place you put it on, not in the Labyrinthian. So if you put the Mask on, let's say in Dragonsreach, once you take it off you will teleport back in the same place in Dragonsreach.

Rather than create another portable storage mod/house, I decided to just modify an existing one in the vanilla game to keep it lore-friendly.

I've always thought to make the Bromjunaar Sanctuary a base for my character. Detached from time and reality, no one can access it except the wielder of the Wooden Mask. Being an ancient gathering ground of the Dragon Priests, I though it was a very appropriate base for the Dovahkin. A private secret base to you can warp to anywhere anytime. Sadly, the mask's ability is limited to a certain area. With the CK's release, I decided to play around and see if I can expand the function of the mask. After a few days of Papyrus crash-course, here we are...

This mod alters the Wooden Masks ability, allowing the player to transport to the Sanctuary anywhere in the game. I changed the Sanctuary to a "noresetzone" like the player's other houses so it should be relatively safe to decorate and store your items. I also unbarred the door behind so you have now more space to walk around.

Currently, there is a bug in the script that disables the Mask being put back in your inventory when you accidentally drop it in the Sanctuary. The player will still be teleported back, but the Mask will be lost to you forever. So don't do it.

Before anyone asks, I'm using Psychosteve's Dragon Priest Mask Retex.