I tow long distances on undulating roads up and down the coast, a lot of it on secondary twisty roads, never have any problems with bearings.
As stated above do not over tighten the castle nut, sure do it tight with a spanner so the bearing sits then back off and do it finger tight. Wobble the wheel and feel if there is movement in the bearing, better to have very little movement than over tighten it.
I use double lip seals that sit on stainless steel sleeves, very cheap to buy and ensures the seal always runs on perfect surface, very important to have a perfect seal. I only use Japanese made bearings, German and USA bearings are good as well but make sure you don't use Chinese bearings regardless of brand. Make sure you pack the bearings before you install them, no use just putting grease on the bearing the grease has to go through the bearing rollers, if you are not sure how to do this on the palm of your hand google it or buy a bearing packer.
Bearing buddies are good and I use them but again keep away from Chinese made, most are rubbish, I put some sealant when I install mine again for total waterproofing. Bras are a must because the buddies will leak with out them and make sure you push the end of the bra in so it's not bubbling outwards .
Pack the bearings with quality marine grease, I use Lubrimatic Marine Grease made in USA but any quality marine grease will do the job, Install the rear bearing and the seal on the hub, put the hub in the spindle then install the packed front bearing, after you adjust it put the B/B on then pump grease until you fill the hub, when the spring on the buddy starts rocking stop otherwise you will pop the seal. After driving a few miles take the bra off and check to make sure the B/B spring is still rocking, if sited hard pump a little more grease . From time to time take the bra off and check again the spring, pump grease as required but again DON'T overfill.
If you like to inspect the bearings do so before a long trip, I take the B/B off and inspect the grease if it's the right colour and not milky, it means all is well, if you see any contamination take the hub off and find out the reason water got in it .
I have the same bearings in my trailer for almost 5 years now without any issues at all.
In Australia you can't have surge brakes on any trailer combo over 2000 kg (4400 lbs). I have Kodiak S/S rotors, S/S calipers and S/S brackets with Hydrastar electric over hydraulic actuator. In almost 5 years I wore out 2 sets of brake pads and replaced the rotors a few months ago, at the same time I wore out one set of tyres as well.
After a long trip before you put the trailer in the water feel the hubs if they are hot cool them down , if you don't, hot hubs will suck water in, even very little water is enough to stuff the bearings. Quality bearings last many miles if not contaminated, can you remember ever changing them on your trucks?
Don't tempted to use S/S bearings, they will not last as they are very soft.
I hope this helps you guys that have troubles with bearings, of course as others said if you tow long distances don't use undersized trailers, I see that all the time both here and in USA.
