Thanks for all the comments guys. This being the first destroyed tank I've attempted, I didn't even give consideration to some of the things you've mentioned.
Whenever I can get my bench back, I will try to somehow change the ash. Ironically, the first time around, the piles were about half as high, but looking at pics, it didn't look big enough, so I added more.
As for the heat and rust, the idea was to show that most of the damage occured on/in the rear of the tank, and besides a large initial explosion, there was not much damage done to the front. I tried to base it on some pics of modern-day T-55 tanks, and I've seen a few examples like this. Although, you are right, and there seem to be more that are just completely rusted/burnt over.
As for the rust, and burns, it was a fairly lengthy process. That part alone took me as long as all of the other construction and painting together. I started by painting the damaged sections in a dark hull red/dark brown mixture. From there various lighter and darker shades were sploted all over. The lower hull and wheels were sprayed with a dark brown, almost black shade, to represent the soot that would have gathered from the burning tires. From there the upper hull was covered with several different colours of orange, red, and brown, in oil colour, which were then blended and streaked. When this was fully dry, the model was coated with chalk pastels and pigments (more chalk pastel than pigment)
One other thing I learned with this one; painting figures with oil is just fantastic. Those who haven't tried it yet, you're missing out.
Once again, thanks for the comments guys. Lots to think about and improve on the next one.