Smooth curve in box steel

[Mith]

I've never seen it done before, hence my asking. Is there a way to put a smooth curve in 1" box, like a rolling machine you use to put a curve in sheet, only for box steel?

I've been toying with the idea of putting some bars from the roll bar on my tractor curved down to the front to make a cab, I'd like the front screen to be curved so I can see the loader when its lifted (it lifts higher than the roll bar).
I added a picture to give an idea.

Is there a machine to do this, and is it something I can make? Or is there a better way to make the curves, I'd only like to make 2 curved bars for the cab, so it seems a little unnecessary to make a whole machine just to do one job.

Thanks for the help.