Be careful with Tectyl. For chassis protection OK, but for internal body protection I'd use something else, especially on older vehicles with poor factory protection, and have probably already started rusting.
In my experience Tectyl and other heavier waxy products dry too quickly and don't have the penetrating capability of less viscous products. They can also build up very thickly with over zealous and/or repetitive application, blocking drains, and creating water traps.
But, Tectyl don't stink like fishoil.......
Also, you really need to think about what you are trying to achieve. I see many vehicles with great coverage all over the outside of chassis rails, and over flat/smooth internal panel surfaces. Unfortunately, these are nopt the areas that rust, at least not critically. Rust starts in areas where panels come together (spot welded flanges), welds etc etc. So make sure you get the product into these areas, and clean those spots beforehand if it's at all possible. Standing underneath a vehicle on a hoist and painting everything you can see with a thick black coat of tar does diddly.
