Actually, most of the trailers our company owns have automatic inflation for the tires. A light on the front indicates that the system is sending air to the tires, and should be checked soon. This system has saved me countless service calls and downtime. If the system is maintaining pressure from a slow leak, just keep driving and get it fixed when possible.
Obviously not the same as the link, but a similar system would work on just about any tire with some simple mods.
David