I was lucky and found an almost complete sheet of "Celotex" foam insulation in a skip just down the road, so I definitely have enough for the seventeen (17!) hills I need for the big game. Here are the first three roughed out and the beginnings of a hilltop town.
The shaping of the two larger hills is almost finished, I just need to fill all the gaps and then add several coats of PVA before adding scatter, etc. The smaller hill is a first attempt at a terraced hillside. The walls have been coated with "hard as nails" and then gravel pressed into the surface. I'll need to do this on the slopes of the hilltop town.