In your case, the trailer hub would have to be stationary, just like the upper bearing in your picture. It's probably overkill anyway.
The Magliner hand truck bearings should be 5/8" inside diameter, like most hand truck axles.
In your illustration with the tube, you could use two oil impregnated bronze bearings if you can get a good fit. They are cheap and a flanged type will support the end load. You can get them at McMaster-Carr or MSC.
http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3742