Hi Skyground, I've attached a fixed version of your model, it needed the bottom face to be rebuilt and also a couple of surfaces in the left and right corners. Only one of them actually needed to be trimmed to go into place, the others I extruded to a snap point so the extrusion was the right size right from the start and could just be joined in directly.

- Michael

Hi Michael !

Thank you very much! I think I understand now little bit more)

Thanks for fixed file. I will continue to work on it

- Alex