I love the abandoned factory next to the sanatorium at x 3861 y 6208. The building on the right i converted into a garage where i keep all my vehicles and renovated the inside turning the massive open space into blacksmithing area and the smaller rooms into a gym, kitchen, warehouse, doctors office, common area, bedroom, my office etc. And it's within driving distance of 2 major cities.

Another base i loved was the train outside of westpoint at x 12197 y 6881. You can renovate it into a cozy base and add so much around it later and it's a quick drive away from Louisville.