Where can I put this?

By cab rack, I think you mean "headache rack", a large strong aluminum structure to protect the cab in the event freight tries to crush it.
There are fittings that allow those hoses to be mounted through the headache rack anywhere that is convenient. Any trailer dealer that sells flatbed or headache racks can help you.

 

Headache is what I'm getting just reading the thread

 

Have a look at the flatbed forum, or spend a half hour in a truck stop looking round.

I mounted mine below the headache rack on a piece of drilled angle steel. You may need different streets to get the hose angle.

Or go total boss and run em down the frame , under the trailer . . .

 

Here is how mine are done.