Is your bun neutered? Because i know from experience that eliminating those hormones can really chill out a rabbit. Also, some rabbits are just instinctly defensive, especially if they are small. I found that when my bunny is in a grump, if i sit near him and pretend to groom myself and make him think "Hey i dont care that you are there" They approach you out of curiosity - then once they are near if you groom them lots they will love you (in rabbit world, a rabbit most groomed is a rabbit most loved).

As for keeping them out of trouble, i know just how hard that can be! If you tie the door handle to something or get a lock or something for the door you can keep him out of there, albeit just keep him out of that room.

My boy Dutch had a thing for wires, big fat ultra chewy wires and i had to keep an eye all the time, but just lifting things out of their reach and making alternative toys for them can be effective, like a big digging box (cardboard box with a hole in and lots of digging material) for diggers, or a big ol' phone book for shredders will keep them busy!

Now i've learned to not be afraid of animals even if they are scary, because if they learn that you are no threat they learn to accept you, especially if you bring them yummy treats a lot!

Sorry for writing a bit of an essay, i hope any of it helps