the poly bags will work only if they are covered with an exterior covering--something like mud. The only place I've read of people using them is in building earthen-wall homes.
2011 F350 XLT 4x4 SuperCab, 6.7L, 6' bed, 6000 miles w/ 8' HD Fisher plow
2007 Honda Element LX 97000 miles
2008 Bri-mar 10k dump trailer
2003 Haulmark 6x14 Enclosed trailer