Help to make custom item

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Only been experimenting with all this Model Editor stuff for a few days myself, but what can I say... I simply don't know when to shut up.
So! After importing your .dae file (import mesh, not open), your mesh might be invisible in the model editor if it doesn't have a material applied yet. Click on View>Outline. If you see the name of your mesh in the window that opens, click on it. Now in the options that appeared to the right, click on the three dots under Material and select your prepared material file (.mat file created with the material editor). You should then be able to see your model and save it as an .ent file via "save as".