As far as size goes, mounting to load bars works fine. However, the XL Ruggedized is a big tent as you know and you'll be pushing the limits of the factory rails capabilities. You might consider upgrading to a different roof mounted rack or load bars.
Yeah I guess I wasn't clear in my post, I would have Yakima load/cross bars on the factory rails. Should be more than adequate. My question was in regards to how long the XL is compared to the length of the 4runner rails and whether or not it would work? Thanks for your time with this