I used Woodland Scenics Realistic Water for the effect rather than the Envirotex I normally use. The main reason is that the Woodland Scenics product remains flexible when it dries. The Envirotex dries hard as stone. Again, without the wooden base, I was worried about the foam warping a bit and separating from the resin. As an added bonus, the Woodland Scenics product also ends up lighter. It took three whole bottles for both boards!
To create dams for the edges, I placed a thick bead of hot glue near the top edge of the water sections and stuck down a triple thick layer of tinfoil. I folded the excess under the board and sealed all of the edges with painters' tape. I smeared the inside edge with vaseline in an attempt to keep the resin from sticking to the tin foil and it worked fairly well, but I still needed to use my knife to clean up some of the edges when I removed the dam.
Now it's time to start adding the next layer of grass effects and make the bogs look a little more wild. I am very happy with how this has turned out so far. More soon...