I'm running my factory plastic tank in my '77 without any issues other than how small it is. I just reinstalled it after my rear axle swap and it was spotless inside...cleaner than I expected it to be, but as it should be. My brother runs a 19 gallon poly tank in his Toyota from a 2003 Chevy S10 Blazer that ended up being a nice, clean swap. So long as they're retained and protected from rock hits, they seem to do really well in general.