It would be great if i can define a minimum of foundation it needs to get protected.

Otherwise you can pump your tc full of scrap in a 2x2 or 1x and put all your loot there, then its like a safe. Protection lasts for ever.

Not exactly the same, but in 1.2 I added the option for setting a "Minimum cost", so if you want you can set it so a 2x2 still costs a pretty penny and you might as well make it into something bigger.