After nearly 1k of driving through salty winter without any arch liners (its on the to do list) I can report that the components that have survived the best, and show absolutely no signs of any corrosion are those which I brush painted with epoxy mastic 121.
I did the whole backside of the filler area with it after spending an hour in there with a grinder luckily for me I caught it before there was any major corrosion but I can 1000% recommend painting areas like that in epoxy. Its dead easy, looks good and protects the area fantastically.
My ARB I had ground back, then coated in rust converter (fe-123) then satin black then clear dinitrol, that has started to corrode very slightly. I believe the flap disk ended up polishing rust up so I trapped rust, the converter seems to be suspended in latex and the light coat of clear dinitrol just sits on top.
All the areas which were done with epoxy first followed by a wax (I used various Dinitrol products) are absolutely as they were and I expect they will be for a long time yet.
Next up i'll remove the sill covers, clean up and expoxy coat these areas too, luckily for me the black epoxy seems to be a decent colour match for black gold... just without the flake obvs.