He's 1000 miles away and gone for 6 months at a stretch. It's most likely oil or coal work. As there are rigs for oil, there are also still what are basically migrant towns for inland oil work and coal mining. Nobody wants to move their families there.<quoted text>
That's mere speculation.
(Since it's only 1000 mile commute, I don't think it's civilian military contracting, which is what my BIL does. He's been doing six-month stretches in the green zone. Six months here, six months there.)