The black coating on OMIX ADA parts doesn't last all that long - maybe 2 years. What my local body shops guys do is scrub the crap out of it with somekind of soap, rinse, dry, rinse while scrubbing, dry, phosphate prep, rinse, and then prime, base coat, top coat (or 2) then clear coat. On the inside of my panels on the CJ, I brushed out what rust I could and then soaked the carp outta them with PR-15 phosphate (Metal Ready), rinsed twice - dried then used the rust inhibitor primer before the POR-15 top coat.
If you use the POR-15 not all of it is UV stable :shock: That was the warning on the can I used to paint my axles :smile:
For the under-body, I kinda cheated - after finishing all the rebuild/replace, I sand blasted, did the Metal Ready treatment and then sprayed on the rust inhibitor primer :t:

The I did the undercoat before it went to the paint shop :?