Hi Ed. With proper maintenance, the cables can last for the life of the trailer. They should be inspected annually at a minimum. The greatest cause of failure seems to be rust that causes the cables to break, usually in the area where they go over the top pulleys at the top edge of the lower half. To inspect them and maintain them there, you have to remove the inside trim strip that is at the top edge of the lower half. It's held on by screws. Once off, you can see the top pulleys and the cable that goes over them. If they are not frayed or rusted, you should lubricate them with something like WD-40 that will run down both sides of the cable from the top pulleys. Then, replace the trim strip.
Next, crawl under the trailer and inspect the cables there, cleaning and lubricating as you do.
I've got a 1707T that has the original cables. But I live in Aridzona and don't have salted roads or high humidity.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew