I think I will try this out on my son's property this year, but I will use a larger plastic can as an added water barrier and place straw on the bottom of the plastic can to insulate the bottom and raise the interior can. I'll keep the lid of the outer can at a few inches above ground level. I live in Florida so digging down often causes water to rise. Our aquifer can be a few inches below the surface to just a few feet.
Last, I'll put the veg in, the lid on, cover the trash can 'cellar' with straw and then cover the straw with a plastic cover or tarp. I will also be placing the cellar on the north most facing part of the property. When you live in the cold North it is cold on all four sides of the house, but for Florida it is imperative to cool any structure to look to the north.
Also for the 'anti-digger' I offer this entry. This photo is from a blog of alternate material builders. They use corn cob, straw bale and mud as well as beautiful interior wood trimming. Browse the site and find the oldest photos showing the footers for a straw bale building and much more information. As well as the online visual tutorial they have work shops coming up in Chapel Hill. My only suggestion to the prepper is, if using this as a root cellar, solid concrete slab floors depend on where you build and if you need to let cold in or keep it out. The alternative material in this building is the sod roof insulation. Clever and camouflage!