Hi Malaise,
I'm Francesco and I work for the web area of Inglobe Technologies.
I do not speak English very well so I apologize in advance for any error.
However I think I can help you.

@malaise said:

The last test I've made: a hollowed cube with a glass face. I noticed the transparency disapears when exporting.

Assigning the material on both sides of the glass, the transparency should work.

Best regards
Francesco