If your codes prohibit you from living in the garage, but let you stay outside in the camper, you have the opposite problem than me. In our area, you can't stay in a camper, because that essentially turns the neighborhood into a trailer park, and the neighbors would never stand for it. But, I could put an apartment in the "barn" without much trouble.
Besides, once you have the place plumbed for a bathroom (I'm assuming that's OK), there are all kinds of ways to set up a free-standing kitchen. Reading one of your earlier posts, you were concerned about the small town aspect of people finding out what you're doing. Once again, if I understand correctly, you're not having any problem staying in the camper - so let them think you're still doing that. Keep a light burning in the camper (even though it's winterized - how can they tell?) and put thick curtains on the garage windows.
You asked, "Where do you cross the line?" If you're looking for someone to say, "Go ahead and just do it", then I'm your man - go ahead and just do it. /forums/images/graemlins/grin.gif
That's assuming they'll hook up the water and sewer lines, install the meter or whatever, and let you at least plumb the garage for a utility bathroom. Add a shower and kitchenette after they leave.