That's looking really good, Miss B! Can't wait till you do the final render! There's a couple of options here. First, you can mark seams and do an unwrap on the low poly version just before adding the subdivision surface modifier as I mentioned, so probably at the stage it is in around the 19:32 mark of the video. Once you unwrap the low poly, you can add the subdivisions surfaces modifier and it should maintain the UVs. Another option, if you have already applied the Subdivision Surfaces modifier and don't have the option to unwrap low poly, is to simply add a UVW > Box mapping to the model for a very quick and dirty UV application. You could select and scale down the result in the UV editor after you create the box map. A Cube Projection map is similar to this and would also work as a dirty fix.

Looking back at that tutorial, I really need to update it for Blender 2.8. There are much easier methods I could add to an updated video which would have probably saved you a lot of time. You did a great job though, so no worries there.

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