First up you'll need to create a service for your Damage Waiver charges under Services in your Inventory.
It would be put under 'General Services'
Enter in the Service information (you can also select the pricing structure - flat rate, percent of order, etc)
Most vendors create a new Line Item Group called 'Services' in their projects where they would include all of the services for that project, but you could just as easily add a Labor Service in the same Line Item Group as a Tent to show both your team and your client what the labor is being used for
Here is a video on how the system calculates multiple Percent to Line Item Group services.