Welcome to the forum. This is easy. I would cut some screen and use a glue gun to glue it together. just take some steel wool and go around the edges of the openings You have 3 openings . The filter,heater,and light. This way you can have some ventilation. The nice looking wood hood will hide all that just like now. You like some tree frogs .LOL I don't think they make a screen for hex's. 30 years in fish keeping and i never ran into one. Tree frogs would love that tank.