For rockets that aren't "S" motors, like what the OP is asking about, I would say that a factor to consider is the strength of the tube the fins are being connected to. The tube staying round is what allows surface mounted fins to work.
For carbon, surface-mounted fins in non MD rockets are fine up to 6" or so. In my opinion, it is counterproductive to cut up a nice carbon tube, and lose that strength, just to install TTW fins.
For fiberglass, the threshold might be lower, and for cardboard, lower still. Doubling up the air frame is something that can be done to help keep the tube round, and there might still be a net weight savings.
Jim