I used to have the same model myself and many yachts do, good units, simple, and easy to use. To answer the question I grounded mine to the hull, when I had it on metal boat. On a GRP one I had a common ground point for all the electronics and ran a larger cable down to the common ground point for battery negative. It is important to ground it though and a lot do not. You see this in my books. RE the instructions on a positive ground battery. This is often a warning however relates to arrangements (which I have never seen yet in 30 years on any yachts) where the positive is grounded and negatives are protected with fuses etc
