Yes, thats where I started.. But of course, I goofed and tried patching the floors. Not only did it come out crappy, there was still a good amount of rust left over.. So this time the entire floor is coming out, as well as trunk. They are being replaced by full panels with bracing and rockers, etc. No more thin metal, no more "patches".. Only difference is, I have to be ginger around the 1/4's since they are done
So I am taking my time, trimming, test fitting, trimming etc..
From my experience..
Measure, write down, measure, check.. Openings, distances from other stationary parts, floor, wherever you can really. That will help on reinstall
Proceed slowly, it is much easier to remove metal than put back..
Replace the entire section if you have many localized or rather large areas of rot/rust. The metal around the spots is very thin, and will make your life hell while patching.
Don't be afraid to try it yourself. It's not as difficult as it seems. Just time intensive and tedious really. Once you start putting it back together you realize how not hard the job was (but you do respect and understand the money involved when you pay someone else to do it.)
Best of luck!