The heavy iron tube has a raised lip in each of the two slots so the latch gets caught on it once locked down. If your two slots do not have lips, I would call the factory to get a new tube. The two lips provide a "stop" so the locking latch has something to get hung up on after it is locked down. As campmuch experienced, his latch was deformed, not catching on the iron lips when tightened down. Make sure your spinning latch lever is not bent or otherwise deformed as not to catch the lips on the iron tube. When installing the cover, always unscrew the latch some amount more before placing the cover so the latch lever finds the slots properly. That should help in preventing a bent latch.
I don't know if this is common to everyone but my latch locks with the key only in one of the two upright positions. I place the cover and screw the handle clockwise until it bottoms out. Then I back it off to vertical and try to lock it with the key. If I have no luck, I unscrew it 180 degrees and then I am able to lock it with the key. Once locked, the handle must look like the picture below, fitting inside the cavity, not sticking out at an odd angle.
When unscrewing 180 degrees to lock it with the key, the two raised lips in the iron tube prevents the latch-lever from going too far to maintain a good attachment. Unscrewing a half turn still maintains a good seal between the spare tire cover and RV body.
