Sanded the original red paint/lacker a bit, to roughen it up.
Then a layer of Humbrol 133, and a second one.
Next, use Alu paint (56), spread out on a bit of paper first, and dry brush it over the brown stuff, making sure the brush direction used was the same one rainwater would when dripping off of the thing.
Next, same dry brushing with flat black.
Dry brushing by me is always kinda 'wild' and 'random'... not thinking about it too much, just go paint!
For the texts on the tanker trailer, I just applied some simplified shapes for the letters -it is way too small a scale to really paint each character- after first painting the lighter coloured boxes, not bright white, something close to it.