VACTAN : MOD approved, water based , easy to use, very economical a little goes a very long way, and also primes the metal. http://www.paco-systems.co.uk/vactan.html
I was lucky enough to be given 50 litres of the stuff. 2 litres is more than enough for a LWB Land Rover chassis. Great stuff easy to apply by brush, or even just a gerden hand spyayer or empty winw cleaner spry bottle.