My son brings his Martin on vacation with us often. We have either used Cape Air or a charter from SJU - which use the same Cessna 402 type as Cape Air. There has been no issue stowing the guitar in the nose stowage or in a spare spot in the cabin. Typically he carries it to and from the boarding gate, and he carries it in a hard case.

FYI - the charter group we use (which is economic for groups 5+ and always much more reliable than scheduled) is Charter Flights Caribbean based out of SJU.