I got the magnets glued in, and tested it out.
The magnets do indeed seem to stick the lid down fairly well. Since it's just styrofoam, the whole thing does flex quite a bit right now when trying to lift it open.
Once the fiberglass is on, it should stiffen up and be great. Right now, I'm afraid of snapping it in half because of the magnetic pull!
After testing the magnetic adhesion and opening and closing, I closed it all up, and drove to my parent's house, about ten miles away.
At freeway speeds, the cover did not fly off!
I dropped it off over there, so next time I work on it, it can be in heated space. The next step will be doing some fiberglass on the BOTTOM of the cover. So when I screw it up, and it looks back - so what!.
Then, by the time I get to the top/outside, I'll have enough practice that it should look OK.
I'll also have to make some sort of holes on the underside for the prop stick/sticks. Maybe those could double as a spare attachment point for bungie-cords, etc.