Panel stiffness, Door metal thickness Options

[porschefile2010]

I wouldn't mind some input from the USA if possible.
Down here in NZ 914's are a rarety and my 75 2.0 is the only one I have really been close to and there are no others handy to check out.
I am bare metalling the car to go back to original- so paint strip, rust kill, etch prime etc.
I have noticed when I have been scraping the paint off the panels ( it's had three repaints)that the door panels have a hell of a lot of flex. The rear guards have a small amount, the fronts not too bad, but the doors! Are they all like this. There doesn't seem to be any side bars inside and they flex probably as much as 1/4 inch in the softest patches.
The doors are absolutely rust free and original paint right back to the first coats so it doesn't look like there has been any bodgy repairs.
So, question is this normal and if so filling and fairing must be tricky as it seems a difficult job bogging a flexi surface and then boarding it down to a fair surface?
Thanks

[porschefile2010]

Well if you are sure your doors are in perfect shape and you want to stiffen the panels why not use the old boatbuilding method that we use to stiffen bow sections where you have large unsupported panel areas.
Get a small postal tube and cut it in half through the length of the tube ( so you have two semi circle pieces).
Lay the piece lengthwise on the inside of the door in a tunnel type position and tack it down with some car bog (sparingly) just to hold it in place and then lay strips of Chopped strand mat over the "mould" and resin it all in place. You might even find it better to lay it over the tar on the inside if it is well keyed to the metal.