It's very easy to underestimate what "tight" means. That's why wing nuts are a no-no on a boat
....you can't get them tight enough.
NB: there are lots of two-legged wing nuts on boats, and some of them are pretty tight :-)
It's good practice on land, too, to use proper nuts and make sure all connections are clean and really tight.
The dielectric grease is a good idea, too, even though it's non-conductive ("dielectric" means non-electrical conductive). It's to prevent the intrusion of moisture and contaminants, but the connectors themselves need to make good clean contact metal-to-metal.