You'll have to extrude step by step ("sweeping front"). Here a few tips:
1) when a part has symmetries it's easier (and somewhat more elegant) to make them appear and deal with a smaller portion of the model. So slice your solid with XY and XZ planes, you're left with 1/4th of your model.
2) remove the holes (Geometry > Solid > Remove Face), you'll deal with those last
3.1) mesh the yellow surfaces (2D), extrude them along the yellow arrow (=> 3D)
3.2) imprint the yellow surfaces on the surfaces onto the surface in the back to obtain the orange surfaces: use Geometry > Curve - From Surface > Project to project the curves from the yellow surfaces
4) mesh the orange surfaces (2D). extrude all the element faces (=> 3D)
5) holes: either deleting elements (i.e. a square hole) is enough for your analysis needs, or else you need to delete a bunch of elements around your holes, typically create a pad around the holes (Geometry > Curve - From Surface > Pad) and extrude along the X direction.
6) create symmetries (Mesh > Reflect), merge, check your free edges and voila!