This is how I have finished the inside of the board. Covered in 3" squares and then painted over with some cheap paint from B&Q, test pots.
There are two lower sections which may or may not be useful- not sure yet.
Have decorated many of the 3" squares. Gonna use this side for town/city Quest adventures, but also Deadzone, hence the squares.
Finally I covered both surfaces in antique oak wood stain, the acrylic, water based stuff.
So in next update, will put up some pictures of the board set up for use. With some tiles and some models.