3 ways to apply materials when one is using Sketchup and what you have done
using surface is one of it. It may be faster workflow for anyone but I prefered grouping first then apply materials.
What I am actually expecting for corona plugin to support all mapping workflow whether by
1. Surface or single face material assignment
2. Grouped faces material assignment or component with materials
3. Imported models with assigned materials or proxy objects
In my test, previous plugin autodetect materials and it renders without tweaking.
Now, autodetect is not working as I can see that materials are even applied to surfaces and grouped object.
Even the transsparent glass become opaque which is previously rendered transparent though no reflection nor refraction effect.