I found the Horizon manual online and there is a chart that will tell you what type and size chain for your model. The type of anchor depends on your boat size and the type of bottom you will use it in,
Mine was not present every time. It was strong after running the Gen a short time. But i never smelled it unless i ran the Gen. I assume my AC picked up the gas smell from the aft birth where the Gen sits just outside the wall.