One option for hills that I used for a large project was to not use the masonite, and reinforce the edge with masking tape. We got asked to help out and make 200 hills for FOW nationals two years ago. The hills needed to have a gradual slope, and more rounded looke than what you use for fantasy. The thin edge was bound to break off, but I didn't have the time to cut out 200 pieces of masonite. We set up an assembly line, one person cutting out the hills in a rough shape, then I'd use a long razor knife to get the gradual slope and sharp edge, third person used sandpaper to shape them, and then the last step was tearing off small pieces of masking tape to go on the edge and wrap onto the bottom of the hill. You need to use small bits of tape along the curves, to avoid wrinkles. Sand and woodglue on top covers the tape, and the edges have held up well for a couple of years now.