Hi, I can't decide which GearTracs to get for my Hobie Revolution 13. I'd like them on the front and back gunwales. What sizes would be best? I have seen revos with the GT175 up front, but to me, the gunwales look a bit too skinny. I think the GT90s would be best for width, but what length? Do the GT90-16 fit well front and back? I put a metal rule on the gunwales and they aren't exactly flat, so should I put some kind of backing between the GearTrac and the kayak, like some rubber? Thanks.