Problems with Nav2 tutorial

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I'm trying the tutorial at: https://navigation.ros.org/setup_guid... I'm using Ubuntu 22 and ROS2 humble Everything is ok until the last section, which introduces inertia. Then I get the warning message:

"The root link base_link has an inertia specified in the URDF, but KDL does not support a root link with an inertia. As a workaround, you can add an extra dummy link to your URDF."

And the collision detected entry does not show up in rviz. The instructions in the tutorial clearly say to put the collision and inertia in the base_link tag. Searches seem to suggest that this is not supported anymore? Am I following an out of date tutorial?

My real need is to modify the turtlebot3_waffle to have another scan sensor that overlaps the lidar for work on network analysis, I'm a complete newby to ROS. Any attempts to add seem to cause more error messages.

Thanks.