My M900 tank had developed a leopard skin print due to being sat for a while.
I used a Bilt Hamber product - Deox.
Magic stuff, sorted the tank out beautifully, since then I've de-rusted a number of items and it get rid of even the most encrusted rust. It works quickly, my tank took a couple of hours, even thick rust is gone in an afternoon.
http://www.ukmonster.co.uk/monster/s...4&postcount=28
I've repaired a couple of tanks and use Silver Solder and a narrow nozzle map gas burner, it keeps the paint damage to a minimum.
I buy a small kit off ebay.