I need a large plastic storage box with either a lid or a base which is completely flat.
Most of the ones I can find e.g. underbed storage boxes have bumps on the lid or base.
A Really Useful Box might work, though I wondered whether anyone could think of something cheaper e.g. Ikea?
I'm flexible on size, but it needs to be roughly the size of an Ikea Trofast box or bigger (if you can picture that.)