Sandbags are a big part of a city table I am planning, so I figured it was time to do some experimenting. What I need flexible sand bags, so they will conform to terrain. Enter the chew pouch. I found these wintergreen pouches on amazon and have been using them in my experiments. All I do is soak the bags in glue and then press them into place. A quick airbrush of paint and a dousing in weathering powder and I am done. A word of warning though, these bags come wet, and they smell like the worst kind of wintergreen ever. They are repugnant. Resist the urge to try one just because you bought a bunch. Once you've tasted these, it is hard to even work with them.
Smaller pouches can be found. I plan to use pouches about 1/2 this size for our 1/72 boards.