Leomund’s Secret Chest in GURPS Magic - how?

[Calliban]

We are playing a Fantasy campaign using GURPS Magic as our base system, and one of the players want a “Item Box” kind of spell, which is much like the old Leomund’s Secret Chest from D&D. The Caster can store some items in a subspace container, and recover them as needed; while in storage, items can optionally remain timeless. The storage space is overall pretty safe and can only be accessed through magical means. Ideally the caster should have to pay a small energy cost to keep items there, or possibly to recover them.

I haven’t found any spell similar to this in Magic, not even something like a Bag of Holding.

I’ve seen someone doing it with sorcery by using Payload/Cosmic, but we are not using this magic system in our campaign.

Is there a spell like this, even if more limited? If now, what would be some good guidelines to create our own?