20 years ago I moved from Texas back home to Oregon. I drove a big UHaul van and towed my car on a UHaul trailer. When I went to return the van/car trailer in Oregon City I went over some train tracks and up a steep hill that was at a very sharp angle to the tracks. 4 blocks after that hill some guy came running out of a gas station flagging me down. The trailer hitch had come off the ball. I had no clue. The guy helped me put the trailer back on the ball and off I drove. Not a scratch on the trailer, van or anything else.
Yes, trailer chains work. Properly adjusted they will keep the tongue of the trailer from spiking into the pavement if the trailer ever leaves the ball.