bed armoring the underbody

I have been thinking about bed armoring the entire underside of my truck to really make it rust resistant. I've had a few small rust spots that i have sanded down and then sprayed with a can of black rustolem spray paint but i was wondering if anyone has ever bed armored the underside. I did bed armor my passenger rocker panel when i replaced it myself so I'm just wondering if this would be a sound and budget friendly method to prevent rust

Too much work for no benefit. Simple deal with rust spots as they crop up. If rust is hidden under a layer of stuff that is textured like rust, how are you going to tell the difference ?

If the water (and salt) get behind the paint it can actually accelerate rot. I keep a couple of cans of Hammerite paint around, good stuff. The traditional Hammerite paint takes a day to dry up good (depending on the temprature). The newer water based stuff dries quick, but is slightly less durable. Hammerite is paint over rust (It neutralizes and adheres to rust), a wire brush to knock the loose stuff off is enough, it doesn't need to be cleaned to bare metal.

Then after a few days I paint over the spot with some brush on undercoating as a little added insurance.

What you really have to watch for is water coming through the metal from behind (pin holes or whatever) and getting behind the paint or undercoating. Happens often with the floor pans and a few other spots. Surface rust doesn't really mean much, it is the rust/rot coming through the metal from the back side you have to watch out for.

Loctite (Henkel, Toreson) make some good under body coatings. Henkel is the parent company, they sell under various brand names. Henkel makes stuff that performs as advertized.