I think there is still room to grow for the GOP in Appalachia. Take for example West Virginia. There is no reason for why such a state should be represented by two Democrats in the Senate.
There absolutely is: it's still one of the poorest states.
That is true, but what are the Democrats doing about it. West-Virginia was a one-party state for much of the 20th century, and it is still poor.
The problem is that the Democrats don’t have a coherent strategy to actually help the working class in these regions. Gun control, immigration reform and climate change legislation might be sound policies, but it isn’t going to help the working class voters in places like West-Virginia.
What is needed is some sort of industrial policy, which both the major parties lack.