Nice trailer, but realize that you will never sell it. A trailer is just too handy to have around. Your pickup, and the next couple pickups, will be long in the junkyard and the trailer will still be in great shape.
Running gear failures on a trailer are user error.
You HAVE to keep tandem tires equally inflated. Never let one go flat. At best it would ruin the tire, at worst the trailer will catch on fire.
Other than that, pack the bearings every 5 years/50,000 miles. All it costs is new seals and a tub of axle grease. Wash the bearings and hub, work the grease into the bearing until there is no air in there, put it back together with new seals, and it will run forever. I have a utility trailer I inherited from my dad, and know it's at least 70 years old. It's too handy to ever think if selling it.