Hmmm....Over course of over 20 years of RVing, and owning a total of 5 different RVs in that time that all had the same basic door mechanism you describe here....Have never had this particular issue. Have had other issues with that latch, and am constantly adjusting it, but never had the latch/hook pull away from the main door.
I would try screwing it in with larger screws, if you can. Failing that.....Not sure, maybe drill all the way through the door, use a screw with a nut and washer? I know that'd look ugly cause then you'd have a screw head showing on outside that you'd have to seal up with some kind of sealant. Not sure what other choice you'd have, unless maybe you could use a rivet gun and rivet it to just the inner side of the main door?