Degrease hub and cap use locktite red on lip,install let dry then grease hub.

That's what I'm leaning towards! I don't fill the entire dust cap full of grease, is that ok?

Yes. I fill mine maybe half full.

I seal my caps with a slight silicone touch to make sure first they seal water and second i dont loose them anymore!

Mine would fly off frequently to the point I have 4 extras. Silicone helps but after a year it gets weak and there they go again.

Trailer hubs have lousy tolerances The chinese guy fell asleep that day when the cnc lathe was cutting the bore. Locktite red or even some JB weld should firmly hold them in. I found that if I had the slightest amount of moisture in the hub grease that It would expand way faster than clean grease. Sometimes the rubbers pushing out would tell me to change the grease. All the trips across the US to Fla never had a bearing failure.