Even in Cornwall, smuggling songs are thin on the ground - in fact in terms of traditional ones, I think they could be counted on the fingers of one foot. There are one or two composed in the early part of the twentieth century but I suppose that work-songs might be considered counter-productive in the smuggling industry. I know it never stopped highwaymen, but it might explain why they're extinct and smugglers aren't! With respect to the number of syllables, I imagine the facility to switch from 2 to 3 might make for a bit of flexibility at various points in a line.