How to best deal with an internal transit component that goes back into stock after production is complete?

I have a paint spraying process that involves the component to be sprayed plus a tray to house them in for said operation. We have multiple sizes of tray to serve the different sizes of part being sprayed. Some sizes have fewer available trays, so can often cause capacity issues, so would be necessary to see what trays are populated with parts. When the parts are sprayed the tray needs to be seen as empty to have new parts placed in them.

I’m looking at finding out what is the best way of dealing with the tray. Whether they should be set as a part number, resource etc.

Any help would be much appreciated.

If you want to place demand against the trays, you should do them as a resource. If you do a part, you would have to issue the tray and then return it every time it was needed.