Im really not sure if he's around still, but King Jamie made these kinds of masks 5 or six years ago when I first got into this. What I did was get a baseball helmet (couldn't find a rugby one) and cut the brim off the front. Then drilled holes around for the dreads and added velcro to the top and the pred helmet itself. To keep them on I used thick wire and basically laced them together inside the helmet.
And yes, I was going to add some kind of small teeth or beads to the dreads but I was in a crunch for time haha and also....I used industrial grade foam tubing for the dreads...not a great idea. The whole thing weighs around 15-16 pounds :/