Annual trailer maintenance?

[WBusa]

Hi, folks. I'm pretty new to the world of owning a trailer and would like some advice concerning annual trailer maintenance. My wife rides in the sheriff's mounted posse, so we own a verrry old, small, no-name, twin-axle, tag-along, two-horse trailer, which we use maybe six times a year on round-trips of about 50 miles tops. Last year I re-wired it because the old wiring was falling apart, and installed a new breakaway box that automatically re-charges its battery every time the trailer is hooked up (the old box had to be plugged into a wall to be recharged). My wife is an expert trailer driver, having been doing it for about forty years now, but like I say we've been trailer OWNERS for only a year. Since the trailer is old and used there's no owners manual, and I don't even know its brand. It passed inspection just before we bought it last year.

Having an accident or a mechanical failure while trailering horses is my idea of the ultimate nightmare, so I want to stay on top of preventive maintenance. What do I need to check/do regularly regarding tires, wheels, bearings, axles, brakes and hitch (and anything else?), and how often? I'm pretty handy and have a good collection of tools (hey, I manage to keep my '95 Ram on the road); is this all stuff I can do, or are there some jobs that should be left to the pros? Thanks!