Cargo Bikes

The local fancy food delivery bullits have plastic 80x60 euro boxes on sideways.

The long way they have to be cut. There are lids.
Cost ca 40€.
Long way with cut looks like this:

love this

found this: https://www.euroboxes.net

has all kinds and shapes. the options here - with some simple modifications - would probably do very well. there are variants with lids that are compatible with locks, even.