I thought I would post this, as it may be of interest to some how I did my rust/burned rhino.
Stage 1: start with a rhino (or other vehicle)
Start with the basic chassis. I sprayed this with basic black spray from a hardware store. Citadel paints work great for this and really crack well.
Stage 2: cover it in glue
I know this image looks dodgy (lol) but drop splodges of glue on the section that you want to damage first. I used citadel glue as it smells nice (!!) and I've always found it works well for this. Leave it to dry a little and then start to smear it around using your index finger, tapping areas to make it bubble and crack. One thing that you might notice is that the citadel glue goes a bit wispy in places and creates trails of cotton-wool like fibres. These are a pain at first, but come off easily.
When you have finished a section, it should look something like this:
and when you have done the whole vehicle it should look something like this:
Stage 3: stippling boltgun metal
For the first layer of paint, take an old tank brush and load it up with boltgun metal. Clean most of the paint off the brush so a drybrush amount remains and then stipple (i think that's the right word for it) the paint on gently so as to not obscure the detail below. Work in small areas and then extend outwards. Leave the tracks until last and just drybrush those as standard. It should then look something like this:
Stage 4: random stippling of tin bitz
Next stipple tin bitz randomly. Use a standard-ish amount of paint and try to cover most, but not all, of the vehicle. It should then look something like this:
Stage 5: washes
The best bit :-) Take Devlan Mud and Gryphonne Sepia washes and douse the model in them, ideally so they are runny and mix into each other. Depending on how much you use, leave the vehicle a couple of hours for them to soak in.
Once its dried, add another wash of sepia in selected areas. It should then look something like this:
Stage 6: weapons etc
The final stage involves painting any weapons etc. that you want to add to the vehicle in the same way (minus the glue), and then affixing them. If you wanted to go a bit mad with it, you could maybe melt some edges a bit or add mud to the tracks.
It's then ready for use: