Again I would like to ask some help in modeling approach. How would you model this kind of shape?

I would need to model a fan duct for a 3D printer and I would like to use this model as a basis. I need to remodel the fan to make it fit to my purposes but how could I create this kind of geometry? I have tried to take some basic planes from the original model and I have tried to use Loft + Shell functionality to create the shape but this doesn't create a solid model but it get splitted. Do you have any ideas how to model this kind of shape that hollow from inside?

I was also able to import the original model to Moi3D as a obj file but it seems really complicated to edit the obj imported model. This is the reason why I was planning to model it with the help of some basic planes from the original model.