Did someone tested some product to spray in the bottom of the track to prevent or retard rust forming?

I've tried to do something on the part after the differentia:

- Cleaned up with a high pressure washer
- Sprayed a product that is supposed to stop rust and can be applied directly on rust
- After that used some black anti rust paint to make everything black again

Results seems quite good, now I need to do the same in the middle part (from from to rear axle), I think I'll avoid to do it under the motor.

Did you had some other suggestions? Removing all rust in a proper way can be quite costly, I'm looking to a simple solution considering that the truck it's not used in winter and so it does not have to sustain a lot of bad weather..

Regards
Massimo

 

Fluid film.