I'm probably going to hit Home Depot tomorrow and check out a bunch of ideas, there should be a ton of stuff there. Stainless steel scrubbers, air filters for HVAC units, faucet screens. (but I'd do what I did when I used faucet screens for uh, other uses and blast it with a torch to burn off anything)
It looks like I started something great! I didn't think so many people would latch on to this idea.
I'd stick with metal mesh made for use with water or food meant for human consumption. A lot of non-food metals contain poisonous metals, such as lead, so I wouldn't use those. I wouldn't use window screening or HVAC screens. Some of those are coated in all sorts of things, including plastics. Stainless scrubbers rust and you don't want rust flakes in your lungs. Other than the faucet screens at home depot, I don't know what else you could use from a hardware store.
I suggest going to a kitchen store and searching for something made of metal mesh, maybe an extremely fine strainer. It would cost more, but since this cart material should last years, it's worth it. At least that's what I think.
I've been very successful using only food grade metal mesh for the past two days. I just rolled three strips up, tallest strip on the outside, shortest in the inside, median size between, and I crammed a thin "bridge" across the top between the outer and second layer that the atty bridge pushed down into the center so that they touch. No flavor and it washes clean with soap and water. When I pull it out with pliers gripping the outer "layer" it comes out in a single piece and rinses easily. I love it! No plastic, no fiber, no taste, and reuseable. It's great!
I think for my next one I'm going to change the cart "bridge" by making a variation of the "copper screen" cart mod. I plan on making the center of the bridge the diameter of the interior of the cart, so that it's a circle with two strips on either side for cramming between the outer and middle layer, and let the atty make the cone shaped indention so that they touch for proper "wicking".
When I drop ejuice in, I drip, then tip it to the side to see if I've exceeded it's "holding" limit. If I drip one drop too far, I use the tip of my ejuice bottle to "suck" up a very tiny amount. This keeps it from "flooding" the atty.
The cart does hold less liquid than before, but I was never able to vape a cart "dry" before, so I think I'm just not wasting the ejuice that the poly held on to. Now when the cart is dry. It's really very very dry. While I can't drop as much in, I don't think I'm wasting as much as before.