The 5th Level spell Haunt Shift allows you to transform an undead (that you presumably control) into a 'Haunting Presence'. Which can then operate the object it haunts as a poltergeist if it has moving parts. So, if you had it haunt a traditional crossbow, it could fire on its own as well as re-cock itself, being a function of its form, but not reload itself with a bolt from your bolt case.
So, if you want a suit of Full Plate to clank around on its own for all time... Haunt Shift is the cheap and easy way to go about it. Carriages, Full sets of Armor, Scarecrows, Loot-Hauling Wagons, etc, etc. The possibilities end with your imagination, so to speak. And what your DM allows, of course.