Torby, you can fix that wrap by putting some slits in your box. The wrap is caused by the plastic shrinking as it cools and eventually, with enough layers, it pulls up off the bed. One answer is don't let the stress get that high. Put some slits in the box to allow cooling.

Pump_Jack_all_pieces.stl

Take a look at the bottom of the main Pump Jack piece in this .STL file. You will see tiny slits that relieve the stress as the filament cools. This piece is much larger than your box. And it can be printed in ABS plastic because the slits relieve the stress. And also, the big circles in the I-Beams help make the design look 'real' but they are part of the stress relief.