You might be hard pushed to clamp the warp out of that unless it's referenced to a thick slab of timber or a heavy steel plate using duty heavy ACME threaded clamps, If possible I would go for separation then plane up the base true, PVA then clamp to the actual cabinet bottom and re screw, Not sure from the photo's what timber the thick base is, could be Pine, Douglas Fir or Ash......Or something else.
EDIT: A quick and dirty method would be to cut some slits in that base with a circular saw, about three quarters of the thickness of the wood deep or even a bit more, glue the finger joints and sash cramp/speed cramp between the bottom of the base and the top of the cabinet, using a thick board on top of the cabinet for some stiffness.
Lawrence.
EDIT: A quick and dirty method would be to cut some slits in that base with a circular saw, about three quarters of the thickness of the wood deep or even a bit more, glue the finger joints and sash cramp/speed cramp between the bottom of the base and the top of the cabinet, using a thick board on top of the cabinet for some stiffness.
Lawrence.
