Why even bother asking for advice if you are going to do this lame experiment anyways? But, since you asked... the suggestions people have made are the best - your way will just create excess moisture. I think it is probably pretty safe to say that mantids generally do not crawl into cellars to lay oothecae - rather, they seem to lay them where they will be directly exposed to air, moisture, warmth, etc.Crows - i know from experience that crows pluck off and eat oths that they can find. Crows walk around on the ground alot. Probably best to protect the ooth in a net as suggested or even wire screen.
For hatching oothecae outside my wife and I use a Coconut Oothecae Hatchery i made from the 1/2 coconut mouse homes they sell at petco. Basically we hot-glued 2 crossing sticks in there and put a hole in the center and hang off the ground about 1.5 feet above a plant. This way you can attach many ooths in there and they hatch out regularly when they are supposed to. They are saved from direct sun and rain but they get plenty of moisture, light, heat, air current, etc. Of course they were exposed to parasites and such but 4 out of 4 ooths hatched this way without any problem. I suppose you could crow proof it by attaching a circle of metal screen with staples to the bottom too.
