Yes every year even if you pack them and don't move the trailer an inch for a year re pack them the next spring that is the only way to truly know the condition they are in.
I lost 12 hours of travel time on a 1500 mile (each way) trip to the Easter Jeep Safari this year because 90 miles into the trip we lost a wheel bearing the owner had made 5 trips and never knew they needed to be repacked/inspected. Luckily there was a Tractor Supply Store at the exit we stooped for fuel at so we just had to wait until they opened 11 hours later.
Sometimes I think some of my family and friends ask me to tow their trailers just because they know I will inspect the whole trailer and correct light and bearing issues.