seems like everyone's well conditioned in your house. Do you see how strong that pattern now is with Bernie?
So now I would also suggest having a command to not allow him up on the trailer. If he jumps up just no, down, outside the garage while you work. Break that habit even further.
One thing I would not allow him to do is keep pacing and running if you can, command him to go outside or just go away if he starts getting pushy. Conversely getting him to go to his place like a mat near the car while you're doing things around it too so he can watch without thinking he ALWAYS has to get involved.
phew behavioral work is hard over the internet :P