I've only faced Bowser X twice and lost twice but trust me, you have no choice but spend hours levelling up to fight him. I mean going though the airway 10 times and fighting every enemy there is a pain the the ass.
The first 3 X bosses are no problem if your at the right level (Durmite X is actually easier an the first fight at recommended level), the"I forgot their name" X bros can take awhile, Junker X is very hard and Dark Star X is not as hard as Junker X but still pretty difficult.
Now what I hate most about Bowser X is that before you an get to him. So use might meteor for the first five bosses to your advantage. Dark Star X will most likely be far from strong enough to not be a joke (maybe Junker X(but without the "far from")) therefore fight him normally. For Bowser X just rotate between Jump Helmet, Spin Pipe, Mighty Meteor, Magic Window and Falling Star. (If that's not enough use Yoo Woo Cannon). I don't have tactics for avoiding his attacks.
Now I been almost two years since I last played BiS but I think that might be the tactic to beating Bowser X.