Windypuff's guide probly' states one of the, if not the best. However, I took a slightly similar, yet different route on defeating the Johto crew.
My team was all 100, fully EV trained, best movesets, correct natures, great IV's, the works. So results may vary for you to some extent. However, I used the Gengar, Gyarados, Clefable alongside a Dragonite, Salamence and a Snorlax - mostly just the tank for reviving/healing my party.
I struggled a bit with some luck; but came out victorious, surprised and happy. Haha.
:y: Best of luck.