Either. Can't see anything in the Ducati shop. The Touratech bags look OK but I'm not sure if they accommodate the exhaust box shaping.
I got mine from 'Great Bikers Gear' for about £40 (£60 if you haver the Topbox too). Was really pleased with them, but after return from 3rd, 2 week trip with them (plus a few 1/2 dayers), the narrow, exhaust side one has worn through where it must rub against the internal, box rivet heads? Probably my fault for bad packing hard content at bottom, but it's a point that needs highlighting.
Amazingly I might have found some https://www.ducatiglasgow.co.uk/buy/DUCATI-Ducati-Liner-for-Aluminium-Side-Panniers/96780811A
Okay I found the top-case one for only £72 2x side aluminium £167 top case liner £72 Total all in price, and they are not waterproof!! £406
Same here but without the problems. I use the inner bags when I'm away with the family and staying In hotels or B&B, places I don't want to take the panniers into. For camping I just use 2 bags for life. They fit perfect, can be used when shopping and easily replaceable. Also a lot cheaper.
I do have the full pannier range from ducati but I also have the flexible panniers from touratech. Maybe something to think over in the future. ENDURANCE red by Touratech Waterproof £123 each or for a pair in a number of colours £238.