You CANNOT peel off the old rubber and install NEW. The rough old glue and splinters on the old decking will show thru on the new rubber and NEW rubber will NOT adhere to the old decking/remnants of the old glue. You will have an uneven surface and a Drastically reduced value on your RV. The only correct way to replace the roof is to strip off the old rubber and either replace the decking or glue and screw NEW decking over the old, so you have a smooth surface that will allow the rubber glue to adhere to both the rubber and the decking. THAT is the reason for the price difference---You GET what you pay for. Doug