Version 2!

slightly taller
the "whale's mouth" is scaled down for someone with out mammoth thumbs
(a little too short in my opinion, might change in version 3)
small notch used to test out elastic hinge (still there)
wall thickness is slightly increased because I decreased the tolerance
for the cards, but wanted the same outside dimensions
version 3 (untested)

untested version 3 (without mechanism)
much thinner walls (needs to be tested for strength)
"whale's mouth" made longer
printable upside down (untested, might be sloppy)