The marine clean is just a degreaser, why would you not want to use it (or any alternative degreaser)?
Needing 'rust to bite into' is such a gimmick joke. POR is a physical bond and process; it isn't a chemical bond to the metal and it isn't chemically reacting with rust to stop it. It just uses its stupid patented little 'fingers' to grip the surface, and rust just happens to be convenient because it's equivalent to an etched surface. The metal prep that they want you to use as the second step is zinc phosphate, which is metal-etching, not to mention it does neutralize rust--the top few micrometers anyways. If it needs a physical substrate to bind to, then I give it a physical substrate by mechanically abrading the surface, just like you would for any other paint prep.
I treat these types of products as I do with any other paint product I'm using...I remove all the rust, sand with the grit I need, degrease, and if using one of these 'rust toppers' which I do admit to using (but have no belief or confidence in their efficacy), then I spray the area down with zinc phosphate, scuff and paint.
I haven't used POR, but I've used Eastwood's Rust Encapsulator, Bill Hirsch Miracle Paint, and Chassis Saver which are POR analogs...paint over rust, moisture cured, will stick your lid to the can if you have any paint in the rim, blah blah blah.
I've painted my entire gas tank with them, floor pans, wheel house, leaf springs, and rear axle housing/differential, this was 3 or 4 years ago. Needless to say nothing has peeled off or so much as hinted at peeling off, but there is rust poking back through.