I'm going to look at a 1977 hi lo to bye.The man says it has a plastic roof that is tar coated. Is that what all the hi lo roofs are like? And I want to haul a canoe on top of the roof. Would that be OK? Would it be OK on a hi lo that has a medal roof if not a plastic one? Or are ALL the roofs plastic and tar coated? Are the plastic tar coated roofs good roofs?