It sounds like everything is pretty good. He may just need more time to settle in to his new home. They all have different personalities, so he might just be a more nervous one. Cruising around his cage a lot, going in and out of his hides instead of just staying curled up inside of one of them is probably a sign of stress. It is really a matter of degree. If he stays in his hides most of the time, occasionally switching from one to the other to thermoregulate, and coming out in the evening or at night to calmly explore a little bit and maybe choose a place where he'll hang out in ambush mode, that is a happy BP. On the other hand, if he switches hides frequently, comes out a lot even during the day, and looks like he is training for the snake olympics as he tears around his enclosure, that is a stressed BP.

If he continues to act stressed, one thing that often helps a lot is to add more clutter to his enclosure. This can be done decoratively with fake plants from walmart or a dollar store, but crumpled newspaper works just as well. This allows the snake to feel hidden and secure even when not actually in a hide, and it can make a big difference.

I really think you should give up on the idea of gerbil scenting, at least for now. There is no reason it should be necessary, since we already know he was eating rat pups. And, it carries with it at least some risk that he'll imprint on the gerbil scent, and then he'll only want to eat gerbils. What you should try to do is get some rat bedding, since he was eating rats. Find a pet store (or a friend, neighbor, whatever) that has rats, and on feeding day get them to give you some fresh, stinky rat bedding. Put some of it in, or at least near your snake's enclosure, so he'll get the smell of it and know dinner is coming. Put the mouse in the rest of the rat bedding, to scent the mouse. After your snake has had half an hour or so to get excited about the idea of eating, offer the mouse. The room should be as dark and quiet as possible. Also, offer the food in the evening or at night.