How to attach and mount wheels onto a cargo trailer? I am planning a bike to move heavy things, separate question here, and sixtyfootersdude is doing a cargo trailer that converges to some extent with my goal to move cargo here. I am not sure whether mounting a trailer wheel is the same as mounting a normal tire but bear with it I am trying to organize sixtyfootersdude's question at the same time as solving my own problem, just answer the question in the title thank you.
lantius is almost right IMO.


use a standard bicycle wheel with a thin through axle, supported from both sides. It's possible to make a really simple trailer this way that will carry quite a lot. The disadvantage is that it's wider than a single sided mount for the same track width (how far apart the contact patches are). Small wheels off kids bikes are often available cheaply or free, and will usually carry 50-100kg each for a few hundred km before they fall apart (come fail immediately, but they're free so don't worry about that).
use a single sided wheelchair hub. They are light and designed so the wheels are easily removable, which is handy for a trailer that will be packed away often. But they will not carry much weight (20-40kg each) because bike trailers get used much harder than wheelchairs do. They're also somewhat expensive unless you can find a stock of wrecked wheelchairs.
use a thick axle with single sided support. MTB hubs come in 15mm (Shimano) and 20mm through axle variants, and a 20mm steel bolt the right length is easy to weld onto the side of a trailer and will hold more weight than even a really well built wheel (you could even drill a 10mm hole through it to save weight. But it does need to be supported well as there is a lot of force on it). I have a trailer built that way that regularly takes 120kg or more without complaint. Unfortunately the build page for it is unfinished even though the trailer is ~3 years old. These 20" wheels are expensive($US135 each) because you will not find them second hand but they work. TriSled use those ones on their load bikes rated to over 100kg/wheel.


You will need to use small wheels on a two wheel trailer (or build your own hubs) because the side forces in corners are more than a 26" or bigger wheel can cope with. With a solid build and care when cornering a 24" wheel can work, but a 16" or 20" wheel will just work. If you build your own hubs with 100mm or more between flanges you could use bigger wheels, but you end up with a very wide wheel (you just added 100mm to the width of the trailer without adding to the load space).

Finally, you must look at Richard Guy Briggs' organ trailer. It's a bike trailer that carries a Hammond organ and player.