Going to do some much needed rust removal and prevention to my undercarriage. and here are the products I am planning to use. LMK what you think...

-RP-342 Heavy Rust preventative spray -Military grade (alternative to Pro 15)
-POR 15 Water-based Degreaser
-POR 15 Metal Prep
-POR 15 Rust Remover or Rustoleum Rust Converter

Another, thing I wanted to ask. After I apply the RP-342 can I then use POR 15 Rubberized undercoating to some of my components (wheel wells, gas tank, rockers) without the chance of trapping moisture since I already applied the RP-342 rust preventative?

 

Degrease prior to sanding, then again after ssnding before paint prep coating. all coats should have compatibility, consult with the maker.

 

POR15 really only works well on heavily rusted steel. It doesn't bond with bare steel well at all, so you have to use their MetalPrep product, and then wet it down with water and wait until it rusts before applying the POR15. Additionally, it cures much like powdercoat, a hard solid layer, that looks great, until the whole thing comes off as a sheet with nasty, nasty rust hidden underneath. POR15 works acceptable well for repairs of small rusted aireas, but beyond that, it's really not the correct tool for this job... There are other products out there that work better than POR15, but not of them great. Rust is a PITA...

The 'proper' way to do the job, as practiced by pretty much every professional body shop and restorer, coast to coast, is 2-part epoxy. Sprayable glue basically, it sticks to everything, is waterproof and UV stable. Your local auto paint supply store will carry stuff that will work perfectly fine; it's not like there's 100s of manufacturers, only resellers... You can ask around your local auto body shops and supply stores and they will all tell you the same thing; this is what everyone is using... The problem with epoxy is that it requires bare metal. It sticks like glue, but being glued to rust doesn't help much.

Avoid rubberized anything. It just hides the small problems until the become big problems. Unless you just want it to look good for a couple years...

 

I know I'm a little late to the game here but if you haven't started yet... check out a product called rust bullet. It's a rust encapsulating paint same as POR15 but does not require the critical prep work that the POR15 does. If you have some serious heavy rust, rust bullet also sells an acid metal prep that chemically converts the rust, similar to what the POR15 metal prep is but much cheaper. It can also be applied to pre-painted metal or bare metal without issue as long as the surface is sanded/scuffed up and it is UV resistant straight out of the can. Not that the UV resistance really matters since this would be for your undercarriage but it's a additional feature worth noting. The only downside to the rust bullet is that it only comes in silver, which would require you to topcoat it for a different color. I will be doing this same job to my XJ this fall and will be using the rust bullet followed by a topcoat with rust-oleum farm & implement paint.

Also, I would avoid the rubberized stuff if I were you. All it takes is one good chip through your coatings to expose underneath the rubberized stuff to moisture. I'd opt for bedliner instead wherever you're considering using the rubber for it's superior chip resistance, especially inside the wheel wells. This is what I'm going to be doing for my project as well.

This all being said POR15 can be a good product if used properly and carefully, just wanted to share my opinion