Hi Ron, I had a big 4x4 and under sealed the whole thing with
Hammerite body underseal with waxoyl. I spent two days preparing and applying the stuff which seamed to get everywhere. Result looked superb and then gradually washed away over the coming months.
Someone told me to use something else, can't think of it just now, will go and find the info later if someone else doesn't recommend something in the meantime.
Paul