How to create an adaptation base?

Hi everyone

I'm designing an adaptation base for a speaker to be mounted in the windshield support of an '82 Ford, I did a model using wireframe on CATIA but honestly, I didn't like the result of my creation.
I want the model to be 3D printed so, I first did an attachment for the speaker just to try how it will work, it worked very well but now I need help smoothing the profile.
In the pics you can see the adaptation done in wood, also you can see my model in the wireframe module from CATIA.
Is there a tool (on any software) to create a smooth part to be adapted into another one?
Can someone give me an advice about this design?

Thx in advance