Here are the things every owner with IS and Disc Brakes should do every 6 months. It is all easy to do, and requires no special tools or expertise:
Under the trailer:
1) The manual says to grease the torque bracket every 12 months or 6000 miles. Every 6 months or so I put 10 squeezes of my grease gun in each zerk fitting. There's only one zerk, and its facing straight down from the tube about 8" inboard from each wheel - you can't miss it. Be sure to clean off the zerk fitting or you just drive the dirt inside the axle. I've been doing that for 6 years now and have had no problems. If you put too much grease it just oozes out of the gap in the shaft. There is no seal, so you can't damage anything by putting too much grease. Worse to put too little.
2) Check the rubber springs for cracking. If there is a gap or split in the rubber larger than 3" wide by 3/4" deep, the spring needs to be replaced. A putty knife works good as a test tool. The cracks are always at the bottom, so its easy to see and measure. Morryde have a very good warranty on the rubber springs. But they are VERY hard to replace so you'll want somebody who knows what they are doing and has the right tools to do the replacement.
3) Check the shocks for damage or leaks. Check the rubber shock bushings to make sure they are soft and intact.
4) Check the brake pads to ensure there is lots of wear remaining.
5) Check the brake rotors for scoring. They should be nice and smooth with no grooves in the surface.
6) Check the inside of the tire sidewall for cracks, bulges or damage. Its normally hard to see the inside of the tire, so have a good look while you're under there.
7) Check the rubber brake hoses for cracking or damage.
8) Check the steel brake lines and fittings for damage or corrosion. Check the brake line/hose supports and clamps to make sure they are all intact. A broken clamp allows vibration and will eventually break the line resulting in loss of brakes.
9) Check the brake fluid reservoir and add fluid if necessary.
10) Lift the tires slightly off the ground using the big foot jacks. Grab the tire on both sides and try to wiggle the wheel to check if there is any play in the bearing. There should be little or no movement. Spin the wheel to make sure it rolls smoothly. Listen for grinding noises from the bearing. There will always be some rubbing noises from the bakes pads but that is normal.
11) While spinning the tire, watch the sidewall for bulges and untrue movement.
12) Drop the trailer to the ground and check wheel lug nut torque. If you don't have a torque wrench, buy one! Use it on a regular basis, especially after a wheel has been removed and re-installed.
If you find anything that looks wrong or damaged, or you're not sure, have it checked and repaired by an expert asap. More detail on all of this can be found in the manuals for the brakes, and suspension.
I know it looks like a long list, but its all easy, simple stuff that anyone can do in about an hour. I find it easier to do on a paved surface, but on gravel it works fine with an old blanket. Coveralls, are nice too, but not mandatory.