Hello Richard and Tony I would strongly suggest a careful read of the MSDS in the link above before using Oxalic acid based cleaners. I am a qualified scientist (UTS and UNSW) and through bitter experience have learned to be very careful with chemicals. I have worked in chemical and biological labs for many years, both industrial and research. I have had chemical burns on my hands when I was working in a chemical factory when very young and ignorant and accordingly I am now am very cautious. My injuries could have been much worse if not for protective eye glasses and clothing. I have witnessed chemical burns in others that have required hospitalisation and left permanent scars. It is important to note Oxalic acid can cause blindness, if it gets in your eyes it will burn your corneas. It is a level 8 corrosive which is the same as most concentrated acids. It certainly will clean things, but it is dangerous. It will most likely will corrode your caravan if you do not completely remove all residual traces of it. It does have industrial uses as a paint remover and also works so well at removing stains by combining with metals such as iron in the stains, so it will readily combine with metals such as zinc and steel. It will also react strongly and dangerously with aluminium (and magnesium). So I would suggest it is not used without full knowledge of the risks and protective equipment (googles, impervious gloves, overalls, dust mask) as described in the MSDS. Regards Terry