I did a floor replacement on my vert. In my personal opinion, remove only one at a time to be sure you don't lose your reference points. If you take both out at the same time, you might have a difficult time getting both to fit properly with aftermarket pieces. It's a tough call which to do first - I might lean for the rocker assuming you can keep the floor from getting too damaged removing the rocker to floor welds. The floor will serve as reference with the rocker install, then followed by the floor... You could make the same argument going the opposite way I suppose.

I've not had to replace the rockers but others have and might chime in.