Maybe you can get some relatively inexpensive trailer to put the kayaks on for the meantime. Harbor Freight, Northern Tool and Hydraulic, and such places sell utility trailer kits that are pretty inexpensive (or you can find something used), and constructing some manner of racking for a couple of paddleboards shouldn't be too difficult. A trailer of that size generally doesn't require a trailer braking system.
I have a roof rack that came with my class C. It doesn't seem sturdy enough to me to do anything much useful, and provides no protection for the roof membrane should anything be put up on the roof. I have no idea why they bothered, unless some think they're decorative or something. (There are also enough things sticking up from the roof that it's not easy to locate any substantial cargo without running afoul of a vent or what have you.)