Looking for a simple empty "tray" part

[Bobe]

The stock service bays are great for housing utility parts, but are sometimes too large and the doors interfere with external part placement. I also used to used 6S Service Compartments, but they don't seem to work currently.

However, what I'm looking for is much simpler than either of these parts, I just want an empty "tray" or "shallow bucket" that can be placed as part of a stack.

Consider the Kounotori spacecraft:

The 2.5m service bay is fine for the pressurized section (although it would be nicer to just have a similarly empty part with no doors), but the avionics module only requires enough space for a small remote guidance unit and a few batteries.

Ideally, as mentioned regarding the pressurized section, I'd like to have either several parts of varying heights or perhaps just a procedural part.