I have retired now but I used to play the concertina primarily for Morris dancing but also solo for my own amusement and occasionally in ensemble with other concertinas at meetings of the East Kent Concertina Players.
The instrument was too heavy for me to play for long without support. Although I often played seated with the instrument on my knees, much of my playing was standing when accompanying Morris. Then I used a banjo neck-strap with a snap hook at each end clipped to a ring mounted on black leather straps which goes round the ends of the instrument. The system is not elegant and my friends complained of the colour scheme but it was functional. I though that some day I might make custom straps for ends but I drew the line at actually screwing anything into the casework. This would be destructive, weaken the structure and probably, in the end, pull it to pieces.