We are currently living in a neighborhood in Thailand where it floods four months out of the year. Our street, at one of the highest points in the neighborhood, will get anywhere from a few inches of standing water to a foot or two, other areas in the neighborhood aren’t so lucky where water gets up to 2-3 feet. We have to pass through these areas to get to work and school and they don’t close with regular flooding. This happens 2-3 times a week.

So far to prep our Hilux, I’ve added diff breathers, a lift, and a snorkel. Truck gets though the deepest areas without issue. I get no water in the floorboards but the bottom of the chassis, differentials, and front bumper get submerged regularly.

The thing I am worried about is underbody rust and water getting into areas that it shouldn’t.  Currently the plan is to spray down areas with a bit of WD40 and do a comprehensive service including wheel bearings after rainy season ends. It’s working so far but I’m open to ideas. Maybe a spray on undercoating? I just have to get a few days for it to cure with dry weather…

We cavity wax for rust recalls and warranty extensions. It goes on thick and dries relatively fast. I’ve been tempted to treat by trucks whole frame with it just because I can.

2 ft spray tube. The end of the tube has 3 holes in it to spray all over.

Noxudol Rust Protection Cavity Wax 5 Pack with Free 24" Wand

https://a.co/d/6WbH6P4

That’s interesting, is it like a spray-in insulation expanding foam? Is there a pre-treatment or do you just spray it in as is?

No it’s a wax that hardens. So it’s a spray on liquid that leaves a coating when it hardens.   Not a foam. Not expanding.

Spray foam will hold moisture against  metals. You don’t want that.

This prevents the water from making contact with the metal inside the frame rails. They rust from the inside out because it’s difficult to get the corrosives out of the frames.

Sounds like cosmoline, but wax.

I get that foam is bad, my question was about the application. Does it spray in via aerosol?

Yes. It is an aerosol that sprays a liquid out of a long tube the liquid costs the inside of the cavity and hardens into a wax.

Use a oil based product so it doesn't harden. You need something that is soft and stays somewhat fluid. So it works into cracks and self heals if rock chipped or scratched. Putting a hard wax on a truck just traps salt etc, behind the film.

My current solution is to use aerosol WD40 on potential trouble areas. Sure the parts have an oily film, but it’s been working ok. I’ve only noticed two spots with any surface rust (spare tire swing out and a chip on the paint on the roof which I need to touch up). I have to reapply regularly because my axles and some of the frame is basically getting submerged in flood water on a multiple-times weekly basis from July through November. There’s no road salt here (coldest it’s ever been was probably 70*F) and I’m 30 or so miles from the Gulf of Thailand so I doubt flood water has much if any salt content.

Do you recommend a thicker oil applied versus something thin like WD40?

Fluid Film is what you seek.

Amazon link

That looks similar to aerosol lanolin.

I need to look and see if I can get this stuff in Thailand. Access to stuff is a little weird here.

I'll second fluid film.  Wool wax is another brand name that is slightly heavier and might work better in a hot climate like Thailand.

I bought the spray gun to use with my air compressor.  The hose will reach into the inside of frame rails and body components, and had a noodle that sprays out in four directions.  I used 1 gallon, and there interior of my Ram smelled like wet sheep for a week.

Can you cut it down thin enough to run it through a pesticide/herbicide pump sprayer?

After some more research, I found a mixture I might test out made from ATF fluid, PB blaster penetrating oil (I guess any penetrating oil would work) and dish soap. I don’t mind reapplying frequently during rainy season if it’s more prone to washing off.