1) You don't need a double-walled tent. Regular 1-walled tent will work perfectly fine even in the winter. At least here, in Wisconsin, it does.

2) A tarp is way more comfortable than a tent. Unless you want to hike in Alaska in the winter, or in Antarctica.

3) Hammock (in addition to a tarp) raises you above moisture and dirt. That's a better way to deal with it than bathtub floor, imho.