I want to share this cbg custom built by Muddy Blues Boxes. It’s a fretless 4 string but really a 3 string. What!? Meaning, I put a bass string to be an octave lower than the low guitar string. Tuning G(bass) GDG (normal cbg tuning). Do, GGDG. I have done this with two of standard guitars that I made fretless. I think it sounds cool on a cbg as a four stringer. Scale length is 27”, flat wound strings. My standard guitars are 25” scale so it can be done with a shorter scale. My bass gauge is 80. All flatwound strings. The key is fretless so the low string doesn’t fret out with a slide. My strings are pretty tight but greeted Guitars don’t work well for this style and who needs frets anyway. The action is low enough to fret. Thanks for listening. Look forward to comments and build ideas.