In the example below, an M57 "Clacker," Box Modeling seemed the simplest way to approach the desired shape.
First step for this model was importing a reference photograph. Here it is in PhotoShop being aligned to the grid and pulled around a little to be less distorted.
I've also added two copies of a primitive circle, again from the Add Object menu, and stuck them close to where I need some holes cut.
Now that I have one loop cutting the box in two, I can use Quick Bevel or other edge tools to duplicate it, and move the resulting loops around as needed for the next step.
So instead I'm using the Easy Bevel tool over and over, turning the rough corners into smoother corners.
Carrara's auto-triangulate tools are a mess, so I've manually triangulated most of the mesh -- or, rather, added edges in order to eliminate most of the n-gons. This requires a certain amount of creativity in making transitions from higher detail (such as the now more circular holes), to less detail.
There are as I said a variety of subtle intercuts and plane changes in the original object!
(In Carrara, you can have a reference picture in any orthogonal view. Go to the "Global" tab to import the reference image).
To fit these together, I opened up the preview pane as far as it would go while inside each instance of the Vertex Modeler, and adjusted the mesh being worked on until it fit properly into the complete model.
This is a lecture all on its own. Maybe several! This pic shows a checker texture applied to the entire model to confirm that the UVmaps are clean and proportional to each other (aka, you don't want one part of the model to be scaled much larger in UV space than another).
I'll go into detail on that if someone comments requesting it.
Not textured yet; these are stand-in block colors instead.