I have what looks like a hairline crack on the chassis of my caravan. There is a spot of rust, about the size of a penny, at the top of the "crack". This is my first van and it is five years old. I have only just purchased it from a dealer - is this something to bother them about or should I just paint a little Red Lead & Hammerite onto the chassis and not worry about it? Any thoughts would be appreciated. Thanks.