I sold my Transalp to a buddy who bought some aluminum boxes, nothing special, just a bit bigger than a computer bag. He got some aluminum plate and cut out to the size of the box plus about 4 inches that was bent 45 degrees to form an "L". The bike had screw/bolt stays in the frame below the seat in the rear of the seat and rear frame. He got some rubber gromets and bolted the plate "hanger" he made to the frame, then put more rubber gromets on the deeper side of the box and bolted the box on the plate with the lid of the box folding out and down. He added a few D rings to the outside of the boxes to manage straps that would strap down soft bags or stuff rolled up in canvas.
My XR 650 had mounting stays in the frame as well, you can fasten D rings or other fastners to secure straps.
I had fiberglass bags on a couple "full dressed" bikes, they looked cool, but I didn't like them as they were made for looks and to carry helmets and maybe some wet weather gear, not much else.
For real bike touring, strap on soft bags!!!! I used some waterproof bags, intended for rafting and kayaks, along with a medium size canvas bag that had pockets outside the bag.....very handy to get to items used frequently.
Thing about soft bags, when you drop your bike they don't get scratched, dented or cracked. They conform to fit more stuff in the available volume than trying to pack stuff against a hard side or in a formed corner of a box which is wasted space. Soft bags are lighter than metal or glass boxes/bags. If the bike drops, no harm, no foul, no scratched paint, just know how to pack your jewels. Best of all, you look like you're on a bike trip and not like a deliver guy from New York City.