However I will challenge you on plumbing and electrical. RVs, Boats, and Vans have plumbing and electrical. There are wood burning stoves that are made to be used on small sail ships. If you look at the indian subcontinent water receptacles at the top of the roof is just a normal part of life.

You could just as easily add solar, a stove and composting toilets to your fort and it would become quite livable by most peoples standards.

These are obviously expenses, but it can be done relatively cheaply depending on what level of comfort you personally require. I for one would be fine skipping showers and having occasional power cuts at night.

Getting the services to the property are the most expensive part.

Fully self-sufficient (septic tank, water well and generator/solar) would be pretty expensive but still mostly a case of digging dirt and putting basic components together.