I agree the humidity is not good,
I have been raising meal-worms for over 20 years and have found that
Non-Medicated chick crumbles or laying pellets are best for a substrate for them,
Don't use it whole however, I used to grind it two cups at a time in a blender (the cheaper blenders work better for some reason) till it will sift through a screen wire mesh, This way when you need a few worms a Tea Strainer is perfect for dipping some out and leaving all the food (and frass) in the container, It's also helpful when cleaning out the container,
I have tried about every kind of food/substrate for raising them things like flour and corn meal seems to cause substantial die offs' of worms and beetles the bran and similar food stuffs seems to me to not promote breeding as much as the chicken feeds ground up, I've thought about trying shorts that I remember feeding to the hogs as a kid but have never tried that.
As far as other food and water for them to drink a quarter inch thick slice of potato every few days (as they consume it) is plenty to have a healthy colony and keep the beetles alive and laying.
I have recently bought a hand crank flour mill and it makes the feed into a fine enough powder but does take a lot of work cranking it so will be adding a motor to it soon, The crumbles work best in a blender since it's already smaller there's less grinding, I use the Non Medicated because I have other things that eat the worms like reptiles, fish, and ducks that shouldn't eat the med's
I buy stacking, cheap, shoebox sized plastic containers and drill holes around the edge of the tops where it isn't covered by the box on the top of it, This will allow plenty of ventilation even with adding the potato slice it works out perfect, To prevent problems a closet is good for them and never keep them in a laundry room or room with a water heater or large fish tanks, the substrate will absorb moisture from the air and cause problems..
That's just my 2 cents worth and what I've learned works out very well for me, I know others do things different and it works for them also,
Good luck with your meal worms,