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]

I would be careful glassing the inside unless you are sure that the shape is dead right on the outside. Once the glass goes off it would be very hard to get rid of a bulge. I like the idea of firing some expandable foam in there but again, too much might push the panel out. However, if the beams are only welded at the ends then maybe it will release out under the beams and not point load the panel.
Tricky one isn't it?
And Tom, thankfully, although there was a lot of bog, there is no rust whatsoever in the doors. The only rust I have found is in the gap between the top rear of the guards and the panel that goes across in front of the windscreen. I actuall have a couple of small holes which I am planning to clean up, rust kill and glass!!! I can't afford the whole panel off and reweld thing and I am already overcapitalising the poor little car. But when finished I think it will ,look a million bucks to me anyway. And of course it's the journey as much as the destination which is fun.