While I encourage you to do all you can to help your bp feel relaxed during handling, how successful you are may be limited by your snake's personality. While your snake can learn to better tolerate handing, you can also adjust your expectations. Not all bps are the same. Just because your snake is more skittish than other bps doesn't necessarily mean that you're doing something wrong. That may just be the way he is and, to some extent, how he will always be. Gotta love the snake you've got. Not the one you wish you had.
On an unrelated note, you should reconsider feeding your bp medium rats. Male bps do just fine on small rats (45 - 85 g) for their entire lives.