I used the generator by BitsnBolts, who I believe is a TinkerCAD employee.
I made a box 70 x 120 x 60 (height) mm. The bottom is fine, but the top has two problems when 3D printed.
Firstly, the large plane of the lid has no thickness beyond the top and bottom layers I specified in my slicer, but there is no infill. Consequently, the lid is very flexible and does not support some features I added.
Secondly, the lap joint is 2.6mm too shallow on the lid to fully overlap the matching overlap in the box bottom. Consequently, the lid is not very stable on the box and comes off easily.
Anyone know how to fix this?