I keep my beetles in cups with about an inch of substrate. As soon as I move, I'm getting a drawer system for them. It doesn't take them long to produce eggs. Its waiting for the worms to grow to the appropriate size that takes so long.

As for a dry gutload mix. I feed oatmeal, crushed bran flakes, crushed corn flakes, fruit and veggie peelings from when I feed my sugar gliders, left over bearded dragon food from when I had a bearded dragon (have a whole jar of the stuff) and crushed cherrios. My mealworms grow very well on it, and I now have two small containers of baby worms currently growing up.