[oil pan 4]

If a wheel comes off a trailer its because the idiot putting the bearing hub together didn't have a clue. All light and medium duty trailer axles spindles go together the exact same way, with a one tooth washer and cotter pin through the castel nut and spindle.
If you have more than a 4th grade education I don't really see how someone could screw it up.

The grease in the HF trailer bearings isn't real extreme pressure grease. It's more like rust proof goop.
Do your self a favor and clean the bearings and pack them with some -40F to +500F brake hub bearing grease.

Don't use the cheap 8 inch wheels. The quality of these Chinese tires is very hit or miss. Or carry a tested spare tire, where you put the new tire on and take one of the old tires off and carry it with you and occasionally switch them out.
I have had one of these tires after 150 miles only at 50% load.

I use a load range E wheel in 145/80r12 steel belted radial. No more bias ply junk for me.
I can't drive 45mph. I built my trailer to pull 2,500lb at 75mph. Oh and it has a brake axle.
So let me know if you want to build a real trailer.