I agree about the advantages torsion springs if you have that option. I don't completely agree about greasing the hubs though. The grease serves two purposes, lubrication of course but also water exclusion.
That's the reason I said the hubs have to be totally full but don't over-pump the B/B if that's what you use.
Once water, especially salt water gets in it can get into the bearings and cause corrosion.
If water gets in there any amount the grease will become milky in that case you have to remove the bearings and replace them if you don't they will fail very soon.
Some spindles have center mounted zerk fittings and a grease channel that runs from the rear back out to the front spindle shaft.Those spindles typically have a rubber round plug about an inch and a quarter in diameter and with a raised dimple in the center. When grease is pumped in, it fills the bearing, the rear space and then flows back to the front spindle. As long as that path stays clear, you can pump grease all day long and not blow out the seals. The grease just spills out of the hub. The hub itself has a rubber plug that you remove to grease and replace when done.
I agree if you want to use these but I prefer the B/Buddies because the the rubber plugs are not always totally waterproof . You shouldn't need to regrease the inner bearing if it was packed right in the first place. Think about this how many times do you repack car bearings in 100k miles I would say none. In boat trailers it's water than causes the problem not dry bearings as long as they are packed in the first place.
Although it is possible on other types of hubs to pump grease till it comes out the seal, there are other causes for blowout. One of course is worn seals but also overheated spindles/bearings that can damage the seal. In addition, overheating will expand the grease but also can boil any water assuming the bearing gets that hot which it can.
Seals will last a hell of a long time , they do in cars and trucks so why not in boat trailers? They don't because the spindle will pit with time that's the reason I use S/S sleeves. The sleeve will not pit the seal always runs on perfect surface so it lasts I would say that the S/S is softer material that the spindle so it will wear quicker but from my experience it usually outlasts the axle, even a torsion axle.
In my mind, the number 1 mistake folks make is improperly tightening the spindle nut, usually too tight Each manufacturer has their own recommended method but in general, you tighten down fairly tight, spin the hub, check for tight again ( that is making sure the bearings are seated and thick grease is squeezed out) and then backing off the nut as per the instructions. That can be a 1/4 turn or more..
I agree they get carried away and tighten the nut fully the bearing doesn't sit as it should gets very hot , blue hot and it disintegrates. You tighten the bearing until she sits then back off until the wheel starts to have free play then do it up until no more play. In most cases that is only finger tight.
For routine maintenance I suggest a few things: Check the inside of the wheel rim, especially the back for grease stains a sure sign of a leak. Jack up the wheels and give them a wiggle and a spin to look for excess play or bearing noise.
When trailering , it was mentioned to feel the hubs now and then. I prefer to use an infrared thermometer. The absolute temps are not super important but major differences between wheels can mean there is a problem. On dual or triple axle trailers, the wheels with brakes will usually be hotter than those with no brakes. Knowing what your typical temps are will help in the future to quickly identify issues.
I don't use a thermometer on mine but I feel them at the boat ramp, it doesn't matter how much braking you do the hubs shouldn't hot enough to burn you , the brake rotors will. If my brake rotors are hot I will not back in the water it may warp them I will wait until they cool down a bit.
While I am at it and sitting around going stir crazy, I also want to mention the oil bath bearing systems. Boy did they seem like a good idea. How many of those trailers have you seen with oil spun all over the rims?
Nothing wrong with oil bath they are widely used in trucks and work well actually it's easy to see if water gets in your hub if you use glass or some people use a plastic bottle as soon as you see milky oil you know there is a problem. I choose to use grease always have , it works for me .
Each to their own, what ever works for you and you are happy with.
The system I use needs very minimal maintenance, take the bra off check that the spring on the BB is rocking if not a couple pumps of grease and that's it, I never repack bearings, if you are going to repack the inner you need a new seal as well, you can't re-use the old one .