POR 15 Rust Prevention Coating vs. POR 15 Top Coat

[1973GMCCamper]

Good morning,
I have a 1973 GMC C2500 Camper Special that I removed the bed on and looking to clean up the rear portion of the frame. I ordered the POR15 cleaner degreaser, the POR15 metal prep and the POR15 Rust Prevention Coating. Question is - do I need to put the POR15 Top Coat on as well?
Also started wire brushing everything that I can reach without major disassembling.
Thanks in advance.
Steve

**Background on the pickup - My Grandpa bought it new in 1973 and he passed it over to my Dad around 1994. I picked it up from my Dad around 2008 and it's been in Western Nebraska since then. Two years ago, I had it shipped up to Michigan and slowly getting it restored. Had a new exhaust put on, new tires/rims, steering column rebuilt, motor and transmission recently rebuilt (454). Front end suspension all replaced (upper and lower control arms, etc) New doors, front fenders/inner fenders, hood, tailgate. Bed is in good shape but will have to repair the back floor area as it has a few holes in it from rust.

 

[PrairieDrifter]

Apparently the rust treatment isn't uv rated. It needs a topcoat of some sort.

 

[Ricko1966]

Okay I'm going to put this up just as general information,do your own research. ( not directed at O.P. , info for everyone). I have always believed that the magic of POR 15 is the metal ready, I've put up a pic of an ospho msds a por 15 msds and a scientific description as to the use of phosphoric acid/orthophosphoric acid one of its primary uses is rust treatment,and metal coating. My go to is clean thoroughly with a water based cleaner, spray with ospho then top coat.