Good for rooftop tents too:
Whatever size of load bars you get, you can always customize the length by sawing them down.
BTW, I've also hooked up the snowboard/ski carriers (Thule and Yakima) directly on the O.E. crossbars.
I've been using Thule rack system on both my LC200 and FJC. Get 2 "Load Bars" in the length you need, and 4 "CrossRoad Railing Foot Sets". Post #13 on this thread from a few years ago has info on the Thule parts: Thule roof rack kayak carrier pics - Toyota FJ Cruiser Forum. I use the same...