Anyone using a Horizon 7011 Cargo Box????

Hi all... I have transported 3 bikes on top of my 2012 Prius with Yakima Whispbars. However, I am, for whatever reason, a bit nervous about transporting a recently purchased SportRack Horizon Cargo Box (7011). Horizon M | SportRack US

The purpose of this long of a box, it's 88.5 inches long, is to transport all our cross country ski gear, downhill ski gear, snowboards, snow shoes and gear that goes with it when we ski. My cross country skis are 85 inches long which led to the 88.5 box length.

The Whispbars are 23.6 inches apart (on center) and the SportRack box requires a minimum 23.6 inches. I am considering moving the Whispbars to a 27.5 inch distance because of the box length.

I am hoping someone out there has used this box/roof rack combo with their Prius and can give me some feedback on how it went.

I would also take opinions on moving the Whispbars apart by four inches.

Thanks in advance