Ball Loosened, Use Loctite?

From time to time my son or I have to tow bar
his 1946 Chevrolet 2 ton rack truck. He uses it
for his food catering business.

Being it is old it breaks down once a year. So
when booked to do a party he has to get his truck
there so it is towed with a Chevy Suburban.

Well the truck just had to have the head R&R so the
truck had to be towed a few times. This time I bought
a new draw bar and 2" ball to get the tow bar level
when towing his old truck.

The problem is that the ball came loose after a few
tows. Last year we had to tow his truck for many weeks
because his engine was at the machine shop getting
rebuilt and we never had any problems using another
draw bar and ball.

I did not have a 1.5 wrench so I went to my neighbors
house, retired mechanic. He tightened down the nut
with a long combination wrench. Then doubled up the
wrench and gave it another tug.

Any ideas why it loosened?

He used anti seize grease when tightening the ball
to the draw bar. He said incase you ever have to take
it apart. I never did that before.

Could that of caused the ball to loosen?

Is it a good idea to clean off all the threads and
apply Loctite?

Thanks for your help.

Here is a link to my son's website so you can see his
truck:

http://www.pizzarita.org/