That is one sweet-looking trailer!
Bearings, tire dates/condition, lug nut torque, running
lights working,
brakes if equipped, coupler latch adjustment.
If you're going to use any
propane appliances, a pressure drop test is a good overall test of the system. You can also test each appliance and smoke, CO, and LP detectors (you have them, right?) with fresh batteries as needed.
Safety first.