I'd be a little concerned about failure of a powered door. The thunderstorms here sometimes cause some weird things to happen. Power goes out, batteries die, motors burn out... Dogs don't understand that kind of stuff.
Remember seeing some rare earth magnets with a hole in the middle, rectangles, on a surplus site. Don't remember which one, but they would be perfect, and cheap.
I use to send my last dog out during hurricanes, even walked him once while the eye pasted over. He was about 130 lbs, so it wasn't that bad. He didn't wander either, don't remember how many times I left the front door wide open and went to bed.
My lab is about 70 lbs now (1 year old), but I'm sure he'd be gone in a flash. He likes to explore.
Anyway, simple and reliable is better for something like this. If you really have to the cool motorized version, I'd suggest using sort of a minimal strength gear motor. One you can turn by hand. If something goes wrong, least the dog might have a chance to free himself, or at least not be seriously injured.