Bagger/dresser whatever... just picking on semantics
It don't matter as he is going to be more comfortable and able to tour or ride with less issues, so good on him!
A set of old Shoei bags would be period correct as would a set of Busco. Pelicans are nice but pricey, but their utility outweighs the price at a certain point. Have a set of canvus liners for your bags made to allow you to haul groceries or other stuff and unload by grabbing the liner's handles and lifting it out.
Adventurer rider webgroup has lots of guys showing building their own panniers out of metal and wood or wood clad with metal skins, etc. Custom solutions that way, but lots more work, perfect winter project.
David