How to make an outline to a thick one line curve?

Is this possible:

I have a C-shaped one line curve with 120 px line thickness. I would like to make exactly this curve object as an object with an editable outline and a fill-in color area (like a default rectangular).

I tried an Intersect with a rectangular but the result is only another thin curve.

The reason why I want this is scalability: if I resize my C-curve, the dimensions change since the thickness of a curve doesn't scale.

Does anybody have an idea :)