I always use never seize on all bolting.
It is standard practice in the Nuclear industry.
What holds it together is the bolt stretch when torqued to spec.
Trailer balls are at least 3/4 fine thread grade 8 material and require more torque than you think.
I'm thinking you did not have near enough stretch to keep it in place.
Check this chart out, a zinc plated, non lubed 3/4 fine thread needs to be torqued to 378 Ft. Lb.
Best way to mount a ball is, on the back of the truck and about a 3 foot tool.
Then give it all you got.

http://www.repairengineering.com/bolt-torque-chart.html

Don


1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!