Depending on the conditions, I've always favored going to ground. It must be the spelunker in me, but nothing conceals like good ole earth. I've seen synthetic designs that, unoccupied, would be nigh impossible to detect from the surrounding terrain, and occupied would likely only be noticable by the comings and going of the occupants, or by heat signature if someone were using thermal imaging.

I always wanted to build a subteranean dwelling, either beneath an existing structure (as an escape/evade device), or as a retreat in a shtf situation. I think it is a really practical idea, and much more secure than the typical surface structure, all things considered. If I could borrow or cheaply rent a backhoe, I reckon I could build a fairly nice hooch with some big culvert and some accessories.