Barney,
In the 1881 english Census for St Pancras, Marylebone, there are a large number of Gumbles 'living in tents' living with Lees, Smiths and a Read, at the end of the census district.
One of these 1881 Gumbles, Phoebe, listed as a hawker, wed Romany hawker Stephen Clark in Horsmonden, near Tonbridge, on 28/09/1891. It seems from this that the Gumbles must have come south at some point, maybe to pick hops in Kent. If this happened once, you can bet it was a tradition to do it regular, as it was for the Clarks.
Hope this helps
Neil