My Rhino extreme hose ends did not want to fit in the rear bumper either
Take a dremel or a coarse file and grind some of the tabs down a bit on the fittings. They are on there to give you additional gripping power only.
Then it will fit without issues with the ends on and the caps on
No leakage in the rear bumper either with the caps sealing it all up!
Just my simple solution!