One thing to be careful with, I believe the Rtics run just a tad bit bigger than their Yeti counterparts. If his Yeti 65 pretty much friction fits with the hatch closed I don't think you'll have room for an Rtic 65. So you may have to either splurge on the Yeti or look into some alternatives like Ozark, Pelican, or Orca.
Edit: Just double checked and the Rtic 65 is almost 2" wider than the Yeti 65. 1.625" to be exact.