What if you were to grapple someone and stuff them in the chest? What kind of grapple check would that take?
How long would their air last?
Can they break out with a strength check? If they succeeded, they be stuck on the astral plane?
I suppose that you could stuff a person down the chest if you managed to render him/her helpless in a grapple, and moved him to the chests square. Personally I would hold the person to get stuffed down there at gunpoint (Wandpoint? Crossbows are hardly a threat to anyone but peasants, and who want to catch peasants?), and order her to climb in there herself. Also, because the chest contains one cubic foot of material per caster level, I would regard it as extradimensional space and thus not allow characters to escape from in there by the means of abilities that does not normally allow planar travel.
The air supply will be quite limited, however, and I would definitely not allow living creatures to survive in there for long.