scotts...that's a great idea with the roundbar!
I've ordered the spring nuts from:
Do it Best
They should work with the Yak Block heads.
I noticed Yak has another item called
BEDHEAD that may work with the TITAN. It just clamps to the edge of the bed. I don't think it'll work with a tonneau cover installed, however.

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2004 Nissan Titan Crew LE
Born on: 03/04
Deep Water, Sunroof,
DVD, Rockford Fosgate,
4x4-Off-road, Big Tow, AstroStart Starter
Overhead Racks/Bed Extender/Divider
TruXedo Lo Pro