In girth work yes, this is why Kegels are so important, the strength and endurance they deliver is not only important but necessary to making girth gains. I would also say there is a second protagonist, being Bundled Stretched. These prestretch the tunica allowing for much faster gains. The tunica is very dense and with prestretching the tissue you will loosen and allow for the penis to hold more blood which will bring thicker girth.
SRT is the best possible girth work out.