I used to like using 3203x on coroplast. Since I've been testing Arlon 510, I've started using it on the coro and would probably use it instead. I outsource a majority of our coro now so using the cheapest stuff we got works for us. I don't even laminate it. I either perfcut it on the plotter or trim it by hand at slap 'er on. I was flood coating coro with cut vinyl most my youth, so I don't really need the air egress.
Most of the metal signs we do get 4600lx/3420 combo or some type of cast gerber/3m cut vinyl.
I will say, I'm not a huge fan of the 3203x anymore. It leaves a lot of adhesive residue during removal. So we had switched to ij40c but didn't like the price and fell in love with 4600lx after a rep showed it to us. So the 4600lx replaced our 3203x, ij35c, and 40c rolls. I also don't like the Biteline UV shield laminate. The 3203x/UV Shield shrinks like 1/8th inch pretty fast. So we've switched to the Arlon 3420/3220 laminates. Now we're in the market for a cheapo roll like the 510 and have been happy with the DAF Safeguard if we need to laminate cheap stuff or super short term graphics.