Sally 4th Sectional terrain system a try, via their recently completed kickstarter. The "Terra-Formers" are a neat concept 1 foot square laser cut box frames that are held in place with magnets (round ones placed in the precut holes. The interior of each frame is filled with Extruded Polystyrene foam (EPS - aka insulation foam).
There are 33 unique types of terrain squares that allow you to incorporate hills, caves, rivers trenches, etc). Given this years painting challenge now has a terrain aspect, I suspect you'll see a lot of these on my blog over the next few months.
It took a sheet of 1/4 inch MDF and cut it down to a 24" square. At one corner I glued to pieces of scrap 1x2 to form a right angle. Make sure you use a good quality square to ensure the pieces form a 90 degree angle. If you're off every terra former square will be off.
I need to go to the hardware store to get some EPS and will use my trusty proton hot wire cutter to cut out foam to fill the frames.
I'm really impressed with both the product quality and Sally 4th's turnaround on the Kickstarter - it was only a few months from the close of the kickstarter until I received my stuff.
Nicely done Sally 4th!