I have been wanting to ask the same question, too. I have used Mobil 1 red synthetic in the past with good luck - minimal washout and no "soap". Last year I repacked the bearings with Pennzoil "premium marine grease" supposedly ideal for wheel bearings. That stuff was dark green and very thin when I put it in and it turned into water viscosity and light blue-ish color within a couple of dunks in the water. It went out thru the grease seals, all over the brakes (REALLY NOT GOOD) and all over the wheels. BTW, My axles have Posi-Lube system and I what I am doing with that system (at least I think I know ).
Just went thru all the hubs again (and installed new brake pads, bearings/races as needed, and grease seals on all 4 hubs). This time I am trying the red Valvoline #615, which used to be called Val-plex EP. Supposedly that is good for "marine" use. I hope so.