I have done some terrain, but have never painted hexes. If i were you i would, use spray paint in one maby 2 coats. Keep it thin nad avoid getting it thick on the edges. They will not stack or fit right if you get them all gunked up. I look forward to seeing this finished.
Why not use a rock terrain piece, with some dirt mounds and what not. O well good luck, and for awesome terrain help go to
www.terragenesis.co.uk
Im widigo there also if you have any questions, im a little new so i may not be of much use though.