I did it once.
I was repairing some floor rot and it made it a little easier to do it because the original steps are not bolted to the floor. They are welded to the frame, actually the steel outpost that connect to the main frame. There are two steel members that are perpendicular tothe main frame at each side of the door opening, The steps fit in between these two frame memebrs
You can see pictures of the ordeal here:
I paid 100 dollars for a used set of steps but they were worth every dime.