When you buy a house, you sign a contract. A legally binding contract, enforcable in court. Part of that contract is any Conditions, Covenants and Restrictions that are recorded with the deed of title. This stuff is Part Of Your House, just as sure as the planks and bricks. So you read the CC&Rs, and if you don't agree with everything there, you don't buy that house. Pretty straight forward, really. Civilized.
In your case, you might want to check the CC&Rs for a ban on outdoor auto repair. Very common. And no, I doubt the court would agree that the bus is not an auto, and that you are building, not repairing.
Hey... I'm not a jerk -- some of you guys know that. I just want you to understand what's going on, before you get in too much trouble. If the CC&Rs say that the HA can fine you, then this could get very expensive.
All my best,