Re: galvanized or painted?
Hot dip galvanizing coats 100% of the trailer with a galvanic coating that doesn?t peel. The structure is also open so any water that finds its way into the trailer is allowed to drain out or evaporated.
Paint only covers the outside of he trailer. The inside is bare steel and any moisture that finds its way into the structure will just sit there and eat away at the metal. At this point a failure is imminent, with little to no advanced warning.
Keep in mind you can always paint the outside of a galvanized trailer for esthetics. You can?t paint the side of a non-galvanized trailer for rust protection.
As far as a hubs are concerned, I?d stick with grease.
There are two inevitable in trailers.
1. A seal will fail sooner than later. Usually at the absolute worst time.
2. Seals eventually wear out the area where the seal rides on the shaft. At that point, the shaft will need repaired or replaced.
A seal failure or a lost bearing cap on a greased hub has minimal impact of the drive ability of the trailer. A seal or cover failure on an oil lube is catastrophic. Do not pass go, don?t collect $200.
Yes, trucks use an oil lube system on the highway but when was the last time you saw a truck axle deep in the water launching a boat?