I just use marine grade trailer axel grease. I have several tubes left over from my boat trailer before I sold them. My trailer carried a boat alot heavier than my TT is and also the boat trailer had brakes so I figured if the grease could stand up to this plus the numerous water dunks it would be fine for my TT. Best to remove the bearings, clean out all the old grease and re-pack them by hand. shouldnt need to overload the hubs with extra grease (just waisting $).
*Currently trailer-less but shopping
07' GMC Envoy w/ P2 controller (current TV)
88' Chevy K5 Blazer (soon-to-be TV)
74' VW Superbeetle (1303)