I was weighing in at about 320 when I first bought my ENO Double (yes I am down about 20 pounds now due to CrossFit). I bought a set of 12' Polyester tree straps and a set of 7/64 whoopie slings all from http://arrowheadequipment.webs.com/apps/webstore/ I also purchased a KAQ new river with the deep winter upgrade which totally rocks and keeps me warm!. I replaced the factory rope with the whoopies and connect whoopies to tree straps with a marlin spike hitch and toggle. I plan on getting some dutch clips pretty soon! You will not have a problem. I have been in the above mentioned set up with both my kids thrashing around and I have also hung in it with my wife. Go for it, it is much easier to work with and I cannot say enough about Paul at Arrowhead!
EDIT: also the polyester straps do not stretch.