Rolling like Clark Griswold?  The Motherlode wraps around your passenger seat to create an XL (20" wide, 15.5" front to back) sized platform, complete with strap loops and hooking points.  1/8" metal plate.  Offered in a durable sand black textured powdercoat. Comes with stainless hardware.
 
The following fitments include the rack with a standard size opening: '94-'21 Sportster
 
An optional helmet lock with tamper proof hardware can be mounted to either side - available here: https://www.combustionindustries.com/product-page/helmet-lock-for-racks