I'm wondering if maybe the
Yakima Kayak Stacker or something would work. Totally not sanctioned but I dont see any reason why the Yakima kayak stacker wouldn't also work for carrying a surfboard. You will also need a set of the
Yakima 24H mighty mounts adapters too. The mighty mounts attach to your 98 Toyota 4 Runner roof rack bars and then then Yakima kayak stacker connects to the mighty mounts. I'd also use a pair of crossbar pads under the surfboard too. Worth a try, got an old board you can try out on some back road where there are no other cars....????
