RP Saloon Sill & Floor Repairs

[Chris KC]

Some time in the coming year I need to address rot in the floor of my RP.
In all honesty I have yet to make a comprehensive assessment, but I can confirm there are areas where the road is visible below. 
I think it more than likely that the cills/ sills will need repair or replacement. 
Probably rear arches too.

My question is, simply, can anyone point me to any helpful how-to's, write-ups, or even Youtube videos which go into the nitty-gritty of saloon floor repairs? I've made a basic search but didn't come up with much. I'm hoping to harvest as much wisdom as I can before embarking on the project.

Failing that, does anyone have any helpful experience to share?

Specific areas of interest:
1. Can this be done on the chassis? I'd very much prefer piecemeal repair in situ over a body-off, new floor approach, whatever the shortcomings. 
2. How to maintain door opening shape and dimensions (is it really necessary to weld in braces?)
3. ...and how to avoid locking in distortions which might have been better corrected beforehand (e.g. door droop).

Any thoughts welcomed - thanks in advance.

[Dave Mann]

I have a friend faced with a similar problem on an RN, he jacked the car into it's correct shape then welded the doors in place while he replaced the sills. he never explained how he got into the body to do that.

[Chris KC]

Thanks Dave, that's very much the kind of thing which is of interest. 

It might be a mistake to weld up the floor and then hope to correct the door openings afterwards...

One side at a time perhaps? I think it would take some bravery to have both sills off at once.