Francine, the black 1020 trays I just ordered are far more sturdy than the "usual" ones you get for $1-2, and the humidity trays are also a lot sturdier. The description for the Mega Heavy Duty trays shows 1 grown man standing in a tray and being lifted by 2 other guys. I was just saying not to have similar expectations for the humidity domes. But I would bet that both of them are sturdier than what you have.
I would try to deter the cats with citrus or herb scents (either essential oils or actual plants), in case you can't get the gravel everywhere. I'm going to see if I can propagate my mint and plant it around the veggie bed to keep the bunnies out, same idea.
