So what is the problem? Well, the photos I have been able to take look awful. There is no exposure setting that can really show the dark areas, while maintaining any light. There is no setting that shows the light areas properly at all. The best I can do is fade the whole thing to a light colour which totally wipes out the contrast. It looks like I've done a crappy job.
My next hope is to combine images with a HDR package like GIMP (Gnu Image Manipulation Program). HDR stands for High Dynamic Range. Computer programs, or the cameras themselves, combine several exposures to produce a range of exposure that would not normally be possible. Here are three images I took at different exposure settings. Firstly, the one the camera wanted, next -1 exposure value, lastly -2 exposure values.
This is the image my camera wanted to take. It has totally zapped the contrast. Those areas that look a little darker in the photo are really dark, with that yellow colour dry brushed over showing up the zimmermit.
Second photo at -1 exposure value.
The tanks are from Old Glory USA.