The plastic material used by Rola is most likely high density polyethylene. Polyethylene will lose strength and soften at 200 deg. F.
I use the heavy duty Rola steel carrier with my 2012 Edge. The exhaust nozzles are lower than the bottom of the carrier frame and have not caused any heat problems. Just to be safe I installed aluminum flashing laced on with stainless steel tie wire under each end of the carrier. Without over heating I have hauled Igloo coolers, folded deck and lawn furniture, and a 200lb wild boar that I shot dead in Louisiana.
I spliced the lighting module power lead into the rear power outlet. Attached is the wiring diagram. Ford Edge Rear Power Outlet1.pdf