Sorry if this is a dumb question, but can anyone please explain to me the dynamic / static weight loads on racks / the car itself? I have a gutter mounted Expedition One mule ultra roof rack and their website says it has dynamic / static weight load of 250lbs / 500lbs. What is the weight capacity on the roof if it is gutter mounted rack? The rack weights ~50lbs. Will I be able to get a RTT?