Universal JLTW 3 12" universal adapter ring.
Tons of options with this from saddle bags, trike trunks, freewheelers, tour packs etc, just shape how you want them to fit.
These have a depth of 2" and an over all depth of 2.5" Easily cut down to what ever depth you need
Comes with mounting hardware, Hardware kit with drill bit will ship on all retail orders.
These are Sold as single rings, make sure to add 2 to the quantity to receive a set