[Yeap]

im not exactly a big gainer yet. but in pe we classify the penis in two categories as to what we work.
The smooth muscle tissue and the tunica. and yes the normal manual stretchs do effect those ligaments you feel down by your pelvic floor muscle.
If your lucky like me after a certain period of time you might experience a Lig pop where one of your ligaments back by the pelvis gives out and some of the inner penis comes out.
with significant length gains this inner penis will deform, elongate and change in the way its positioned.
hope that helps