Engine storage

Kind of a simple-minded question, but is it preferable to store a boxed engine/loco sitting upright, or on it’s side? I’ve got limited storage space for large plastic tubs under my train table, and I can fit a few more engines in the tub if I stack the boxes on their sides rather than upright. Any reason to NOT sta***hem long-term sideways?

GPJ

They come in boxes that are well protected with foam so it should be ok, run the smoke fluid out though, or don’t fill it before you store it.
laz57