I would lose the bathroom. I mean, how often do you need to use it. Unless you are living in your train room, that seems silly. I know I only go once a day. Stay away from Budweiser and chili in a can and you should be ok. Or if it is that important put a bump out, I mean separate room addition off to the side. Why not make a trip to the house if the need prevails. I would think the expense of having to run sewer and water alone would be a deterrent. Just my two cents. Hope I am not being insensitive.
Remember pay toilets? Was a dime at the Bears’s games back in the day. I always thought that was cold hearted.
Cheers, W1