If it has drop windows on the head, keep those hinges lubed... I use synthetic motor oil on mine, just a drop or two of oil where the hinge points meet....  Check the bolts that hold the steel wheel carriage framework to the outer aluminum frame rails. I have had some of the bolts to shear off. Have to pull the wheels to get to broken bolts.. Even with the bolts out everything seems to be tight. Other than that, that's about all I've ever done to mine..  Tires, adjust brakes, wash and wax.

  Those drop window hinges don't have any loose play in them, it will take a light/thin oil to seep in between the two surfaces... If they are stiff, it may take a few days for them to loosen up. Try moving them up and down every day or so for a week or two. Never had any trouble with mine until I started leaving it outside.  The bolts I'm talking about are the ones that you see inside the trailer just above the axles on that outer aluminum frame rail. Bolts come through from the outside with stainless nylox nuts on the inside... Probably four or five to the side.

The same synthetic oil also works well on ramp hinges, door latches and locks, window slides, almost anything that moves. Also the synthetic products will last longer and not wash away as quickly as petroleum based products.

If you have a firearm, the synthetic oil is also excellent to wipe it down and use as a rust preventative and lubricant