I've done underneath cars before with various incarnations of black killrust etc. Usually hand brushed on. Time consuming and messy.

The think I've noticed is it tends to go from being a very jet black to a very dark grey/blue grey is a few months. Plus its hard to get into all the little areas with a brush.

Whats a good compromise to provide protection (my chassis is very good and want it to stay that way) but that will stay nice and black long term? The PO used POR15 on some bits (he started then sold the bus) and he said it was a pain to use, I'd probably prefer something I can spray on to make it quicker. Planning to gerni off the underside, clean up any bits that need it and hit it with something.

Also I've used fish oil in a spray can on an old landrover before and it worked well as a rust protection/internal spray protection/undercoat to the paint. I've found that I can swap the nozzle for a WD40 nozzle with the straw and then it sprays inside all the little nooks and crannies easily.

Any tips on what others have used under the body?

I have used various paints

couple I can recommend.

Rust bullet automotive formula with you choice of black top coat, you need to test yourself to see what is compatible. RB auto formula is excellent rust protection, tough and good adhesion. I do find because its a thick paint with super high solids content, chipping can be a problem if constantly pummeled with gravel.

The other paints I like to use is wattle super etch epoxy primer with a good quality epoxy gloss black.

because the paint is quick thin, it only chips localized contact point (very tiny pin prick hole in the paint). This combo is far less durable to chemicals and solvents though, fine for fuel though. I found this very tough overall against rust and abrasion.


2 pak epoxy primer and epoxy black top coat would be one of the best choices. I have not tried this one myself but I have seen cars coated in it, 2 pak epoxy is really really sticky adhesion, very tough, very good rust protection. And it should be less susceptible to chipping as it fairly thin paint compared to POR15 and RB.


epoxy e-coat is the ultimate! there are a small handful of electroplating facilities that do it, not sure they would do a whole pan though

Most of the factory e-coat on 90s onward cars are unbelievably rust protective and takes a shit load of sandblasting from gravel to wear it away, it is also super thin to the point the coating is somewhat translucent sometimes. So tough in fact, a lot of car makers back then didn't bother top coating it under the car, so its only the e-coat doing the protection and still no rust in most cases I have seen even 25 years plus. nothing touches it either, solvents and even paint stripper do nothing to it. only way to get it off is grinding/sanding or burning it off in a furnace at red not temps. The later is how I stripped my bmx parts

I doubt anyone would go to the trouble of e-coating though.