I have a '49 Chevy 3100 with surface rust on the inside of the fender wells and on the bottom of the cab (who doesn't) and was wondering what is the best way to 1. clean up the rust without media blasting and 2. the best and prep for a tough/durable finish for these areas that get hit with road gravel

My apologies if this has been covered already, but I found a few posts on the forum vary from rattle can bed liner to (2) coats of POR 15. I'm thinking of applying POR 15 (brushed on), or some bed liner but i am keeping the existing paint (for now) and just want to stop the rust on the inner fenders and bottom of cab correctly before i put it back together.

Metal Ready and a wire brush sounds like it is good prep for removing loose surface rust and neutralizing the rust before applying POR 15 (no primer needed). Are there any durability issues with POR 15 getting hammered by road gravel, or is it so hard if done correctly, it will be fine? Is there a bed liner that is better, or is that just too thick? Would Metal Ready be a good prep for a bed liner, or does it require a primer?