I reviewed diy ideas online for landforms and ended up melding a few techniques together for what turned out to be a fairly easy project. I purchased cake pans at the dollar store. I had plenty of flat shipping Styrofoam in the garage from former purchases. I cut it into the landform shapes and hot glued it to the pans. I used this amazing Sculptamold product to cover the Styrofoam shapes. Next I spray painted all of them blue, used a mix of acrylic craft paint colors for the land, and sprayed them with polyurethane sealer. (Next time, I would probably use clear caulking along the seams for additional waterproofing). They are lightweight and seem to hold water well. The link I used for my landform cards isn’t working, or I would share that as well.
Of course, it’s even more fun to learn about landforms in the backyard!