External dimensions are 31" and the internal is 27.4". All of our ski carriers come with Universal Mounts included and yes you can remove those and only use the T-Bolt that is supplied and mount directly into c-channels on Aero Crossbars. Thank you and call us with any more questions at (303) 706-9700.-Rhino-Rack
It would really come down to the width of your wakeboard. The 574 has an internal carrying width of only 19.7 inches, while the 576 has an internal carrying width of 27.4 inches.
The rack will fit onto VW factory crossbars and most aftermarket crossbars, the VW Beetle would need to have crossbars.
Yes, Rhino Rack Ski Carriers will fit on square crossbars.