Yes...I just scored an even bigger plastic jug from my recycling bin...lol...asked my GF why she was recycling our new mudflaps...hahaha...that one in the pics is several years old and works as well as when new. I was going to wait until it wore out to replace it with an even longer one, but I may die before it wears out so this year it's getting a fresh milk-flap...

I use mesh bags because I don't care about the dry factor in my Ortliebs and the same ones can be reused for decades. I got tired of throwing out other bags at the end of a tour. I also use the same bags when traveling to keep my stuff organized. Of my 4 Ortliebs I only use this system in my 1 clothes pannier. My other panniers don't need as much organization.

I tend to pack light so I don't run out of space in my bike bags and actually prefer them to be "full" with my expanded gear.

I've used milk jugs for mudflaps for years too.

I used to attach them with a small nut and bolt onto the SKS plastic/Al laminate. On the last few I discovered spray adhesive (or contact cement) works as well or even better. I spray paint mine black to match the fender.

My panniers are water-resistant. I use 30gal kitchen trash bags (occasionally trash compactor bags - they cost more) and Ziplocks to waterproof and organize gear. It's a simple idea that evolved from my backpacking experience, except there I use a WP poncho with long tail to protect myself and pack, plus ziplocks.