The UFP website has some good brochures on it for info. Here is a few things they say:
You can match the grease already in your hub by using Trailer Buddy Wheel Bearing
Grease or use any other good quality, #2 grade multi-purpose grease. Use a water
repellent grease if you’d like, but it’s not necessary because water won’t enter a properly
filled hub. Grease consists of oil, soap and additives. (The soap in any particular grease
has one of several chemical bases [lithium, calcium, etc.]). Oil sometimes separates
from the soap and may leak out of the protector or under the rear seal. This is normal
and won’t create any problems.
There is no need to repack bearings if a good quality lubricant is used and the lubricant
level is properly maintained.
PRESSURIZED SYSTEM WON’T DAMAGE SEALS
The slight (3 psi) pressure your protector maintains inside the hub WILL NOT damage
inner seals. Adding grease with a power gun at a service station WILL damage seals!
Fill ONLY with a hand gun!