Hi! I was searching up crossbar lengths for my 2009 Rav4 and stumbled upon this thread. The EXACT same thing happened to me 5 months ago, where I purchased the EXACT same box and only realized while packing the car that the crossbars have a limit of 102 lbs! From what I've read, the limiting factor is how the OEM crossbars are mounted on, pressure points from the screws that lock it in place. So minus the weight of the box (46 lbs) you only have 56lbs that you can put in the box. Because i was rush rush.. i just put all the blankets and stuff in the stop and stuffed the rest of the stuff in the car.
Now today (a month ago actually), I purchased the set of Thule Raised EVO kit and 53 inch WingBar, which is what was recommended on the Thule website. When I mounted it, seems like it was borderline too long for my car. I ended up switching to the 47 inch (only because the store i purchased them at didn't have the 50 inch) and now i'm searching around if anyone else has the same setup or if I should return it and by the 50 inch elsewhere. The 47 inch does look like it fits fine, about less than an inch left on each side.
Hope this gives you a better idea on what you need to do next! (assuming you haven't already bought purchased one)