Hisham;
I would start by surfing the web for recent burn-out pics from Iraq, etc. and find examples which look most like what I'm thinking of for the project. Each burn-out is actually sort of unique and the color-range will differ.
I would next head to the paints and a pallet - I imagine that using hull red and tan, light grays, yellows and white could give you a lot of possible fired-rust potential. Depending on the burned hull parts, there could also be some sooting (dark grays and blacks) and some ashing (light grays). Having a couple of nice color burn-out pics on the screen by the pallet as you mix would be good!
PS: I am guessing that the tank is some "enigma" version... I'm naïve about it - but what are all of the boxes supposed to be - I keep thinking reactive explosive armor. Can you find any burn-outs with those still intact? Just asking...
Bob