If you have a helper, it'll be a little easier, but it shouldn't be a problem.
You'll have to drill out the rivets in the baggage floor to remove it to get at the ribs and you'll need a right angle drill with a hole saw (or, failing that, a Greenlee punch) to make the holes in the ribs through which the "tube" portion goes, but it shouldn't be difficult.
Whatever marginal increase in effort compared with pre-completion is more than worth it for the result.
Lots of people basically do this anyway considering that steps occasionall crack and must be removed and repaired/replaced.