[.:4:.]

Negative ball weight is bad. Ive left my work car with a box trailer with the boys before to do a tip run and scrap metal run and a few times they thought they were doing me a favour by putting the light rubbish up front and the heavy metal in the back. They meant well, logic being its easier to unload heavy stuff if its in the back, but at 80 on the freeway, hit a bump and the trailer wants to tell the rear end of the car what to do. I never came unstuck, but you can deffinately feel the rear end of the car start to 'float' i guess thats how to describe it. I would much rather tow with too much down weight then not enough. Yes technically that takes weight off the front axle of the car and greatly effects braking as the front wheels do the majority of braking.
But for my personal use i bought a car that suits the boat i was intending to tow, part of the reason i bought it. 1600kg boat on trailer, falcon. Wouldn't want to tow anything heavier with it, but the boat came before the car.