Re: Attaching Hardware Cloth
You might be better off cutting two rectangles along the sides of the tubs then attaching the hardware cloth on the inside of the tub. I've read that ammonia is heavier than air so it will sink to the bottom. This will provide better ventilation then a screened top. I used heavy duty sheet metal shears, cut through the tub like paper.
I used the wire that came wrapped around the hardware cloth to attach it to the sides. No cost to me and no chew throughs. Drill holes run the wire through and give the wire a few twist with needle-nose pliers.
Good luck