Even Vegeta trained on a meteorite to become a SSJ, and he still had to pump up his gravity training to past 400% normal gravity in order to give him a workout. Eventually, even that would not be enough.
In Goku's case, the only real training he would have had with the Kai's and in the RoSaT. But even so, the Kai's training took 10 Tonnes (correct me if I'm wrong) worth of arm and leg bands to even give him a workout whilst in SSJ mode. So what hope would he have had after all that? There was really nothing to keep him "pushing the envelope" as you could say.
What was he going to do, tie a couple of cars to his arms and legs?
Seeing him fight Uub near the end of DBZ made me realise that yes, he HAS been training, but to what extent, and, quite simply, how?
