You can use products like
Dubia Dew and
Roach Chow to keep your dubias fed and watered. Using a commercial chow rather than trying to make your own formula is a good way to make sure they're getting the nutrients that they need. You can also throw in some fresh vegetables like dark leafy greens, sweet potato, or squash to give them some extra vitamins and hydration. Never give a water dish to dubia roaches, as they may drown in it.