Weight training is great if you box, if you have more fat then muscle when you get hit the shock will fluctuate through out your body causing a more intense injury. But keep in-mind, not alot of people can handle too much muscle. If you've ever watched a someone at your gym maybe about 240lb fight, you'll notice he probably hits slower because of his muscle mass. Some people can handle fighting with a large mass, some people can't.
edit:
here's a link that might be helpful to fully answer your question.Are you being serious? If you're going to "weight train", then you should do it correctly. That means adding minimal, if any, amounts of fat while gaining muscle. If you look at Mike Tyson during his peak (as well as Roy Jones Jr) you will notice that both of them have pretty defined abs and X-type lats. Why? abs will really help the movement of your core, which should strengthen your punch. Lats I guess (not sure) are good for blocking the side punches so they don't hit the bone.
Boxing is a skill that can be refined, but some are just naturally good at fighting while others just naturally suck.
You're born with it.
The lats are good for punching power ^^
