I've not forgotten about you Substance Painter...

 I've not forgotten about you, Substance Painter, but I have forgotten nearly everything about you.

So this morning I decided to start a refresh. One thing I didnt understand was how to select difference parts of an object to be treated as a different material set in SP. Turns out I just needed to assign different colours to objects in Blender.

Model the object: A lunch-box

Ensure that all parts are given a material. This way, when exported as a FBX, there will be separate colour for each object.

Import into Substance Painter - Paint!

Once you have exported your maps, return to Blender. 

In the shader workspace, select the material shader, select shift+Cntr+T. This tells Node Wrangler to bring in all the material maps and place them in the appropriate material channel.

A very rough output. I just went with a smart material with no modifications. Next time I'll fine-tune the materials.