I dislike seeing the sunlight shining thru the plastic fenders as I think it makes them look cheap, so I was wonder if anyone has tried something like rubberised undercoating on the bottom sides, and how it looks, and if it stays attached. .

 

I put Herculiner on some boat seats that I was constantly having to refinish each year and replace every 5-6 years. It's a roll on product that you can get from most auto parts stores. I don't know how well it would stick to plastic but it's still sticking to everything I got it on. (I'm a good carpenter but lousy painter) Super strong, stands up to abuse. If it does stick to plastic, you'd probably just have to rough up the underside of the plastic with some sandpaper. I think you can get it in a variety of colors. Try http://www.herculiner.com/product_info.html

 

Moose

What kind of surface? Is it a slick finish surface that is flexible too? thanks

 

It gives it a textured surface that on a flat panel like wood is non-slip. I believe it is pretty flexible.