ok so after going through multiple threads, i now understand what @Xulfiqar bhai meant to say.
i) on the floors (inside), one can apply rust converter, then a primer coating and finally the paint. it should be enough
2) on the underside, we need to scrape off the diesel etc. and then apply the 3M rubberized undercoat (save the rubber parts and engine etc.)
3) the DIY wax is for cavities.
my understanding is correct i hope.
