Plastic wheel well trim looks horrible

The best way to restore them is to paint them.

https://www.rustoleum.com/product-catalog/consumer-brands/specialty/paint-for-plastic-spray/

I would buff that a little with a scotch pad before shooting the rusto. Krylon has marketed that stuff for quite some time and I had good results with it, not on the fifth wheel though.

Krylon spray paint?

I paint them with duplicolor

I'm not sure by the photo, but is that black molded plastic that was not originally painted ? If so, this stuff works great Mothers, Back to Black

Paint is obviously a good solution. You can also treat with 303. Will make them look good but not for long. A friend uses a product, available at Walmart, comes in moist sheets or pads that one wipes on. The name might be “wipe new”, but I’m not sure that’s correct. Friend says it lasts quite awhile and he uses it on plastic bumpers and trim.

X2 on the Mothers Back to Black.

MURPHY55347 wrote:
X2 on the Mothers Back to Black.

Mothers Back to Black is great stuff but on a panel that large, not so much. You'll be reapplying every 3 months or so and that will get old.

While I haven’t tried this on plastic, I had a number of really obstinate brake powder/grime on the wheels of my f150. A rag and some gasoline works fantastic.

My vote is also for painting them. Mothers Back to Black is a nice product that I've used on my truck trim but I have to re-apply it after every couple of washes. Paint them and be done.