JumpCo Portable Warehouse

From the introduction:

While it is true that anything brought from Jump-chan via the jump documents will usually follow the Jumper from one jump to the next, what about the various goods, equipment, and other items the Jumper will collect during the course of a jump? Or when one doesn’t wish to have reason to explain the presence and nature of a mech or aircraft to a medieval king? Fortunately, we here at JumpCo have the perfect solution to every Jumper’s storage needs! The JumpCo Portable Warehouse! Your very own pocket dimension! Comes in three sizes, any colour scheme the Jumper might desire, and with a variety of further customization options!