Tongue of 1972 Shasta very difficult to get off ball.

I had a pound of leftover disk brake grease with a high temperature rating, and it will not run off quickly in the rain. It was also fairly cheap, only about $10 for the pound can.

I put a little grease on the top of the ball when towing. You may need to remove as much rust as possible, then coat the insides with thick grease (only a thin layer, but grease thick enough to not drip off like thin motor oil might). Anything that moves should have grease coating it.

Have fun camping!

Fred.