The choices are:

• Go with saddlebags with no hard support. Cheaper than the other solutions, but these will scratch the sides, and volume will be limited.
• Installing a scaffolding to get side rack in place. On the racks one can attach aluminium boxes or soft bags. This also has the side effect of protecting the back of the bike and most notably the exhaust in case of spills. Can support lots of storage, but can be very wide.
• Installing touring panniers. With small inconspicuous side rails. Those are intended for road use, basically the same hardware as the 790 Duke,  and are less robust than proper adventure side rack. If you don’t plan to do any off roading this may be a good choice.

KTM offers side racks, Touratech panniers, and touring Panniers. You can mount third party bags and panniers on the touratech rails. See the article on third party luggage for non-KTM options.

Black aluminium Touratech panniers for KTM

Touratech side racks are needed, p/n 63512912044 at about £235.

Then add the two side boxes p/n 63512922000 (45 litre) and 63512923000 (31 litre) which are about £393 each

Add the locks (they can be keyed to be the same as the top box)

Total cost £1020. Cost of the complete Touratech setup (side case plus top box) is > £1600.

Warning: this setup is really wide; this makes the bike 106cm wide

Touring Case Set (panniers)

36 and 30 litre, p/n 63512932044, about £700. Needs mounting rails, p/n 63512012044 about £209. Total cost £909.