My suggestion for a minimal retreat located on cheap land, preferably in a forest.
This is designed to be something that will allow a person, family, or small group to have a place in which they can take shelter for a period of time, either to wait out a short-term situation, or as a staging area to get ready to move to a new, permanent location, or to act as the initial base for a semi- or permanent camp or community to develop. Much of those possibilities will be on what and how much is cached in the area, above the primary supplies for a limited stay.
It is a one or two room reinforced concrete block structure with concrete roof and floor, preferably mounded over with earth, or with parallel concrete block walls with 2’ to 5’ of earth fill, and two right angle shielded entrances with simple metal doors. Size from 12’x12’ to 24’x24’, located off any beaten path, and built by hand with materials brought in on foot with a cart, or by ATV or 4WD pickup.
If a gravity drain can be incorporated, one can dig down, and have a good start on an earth sheltered structure. But since there will not be any doors or windows installed, rain and snow melt will get inside. So it must have a good drain. And it should be located in a place and installed in a manner that it is not obvious and cannot be blocked by someone wanting to cause mischief.
It would be furnished with all metal bunk bed frames, an all metal countertop assembly, and a metal picnic table with benches, all securely fastened to the concrete floor and/or walls. Alternately, concrete and/or concrete block versions could be constructed. Might even be able to incorporate secure storage inside them.
Cached close by would be equipment and a minimum of a two-week supply of food, water, and other consumables. A chemical toilet, a portable shower, and other equipment would also be cached. This includes the metal doors for the cabin. Only pieces of tarp hung over the doors would be left up when unoccupied. These you would retrieve for use in the shelter.
By leaving the structure accessible, vandals might trash things a little, but the building and furnishings are fireproof and resistant to easy damage. With a few supplies left in plain sight, such as a small box of canned goods and a few bottles of water, anyone that finds the place will probably just use up the supplies, do a little vandalism, and then move on.
If it is occupied when you get there to use it yourself, you should be carrying the means with you with which you can gain possession. Or at least have them cached not too far away. By building in features to make this easy, you would not even have to have a major confrontation, and certainly not try to run them out with a frontal attack on the place. You want to run them out from inside, in a manner that does not expose you to harm. If you would like some ideas on how to do this, contact me and we can discuss it.
You should be checking on the site from time to time, anyway, just to make sure you can find it when you need to, and that no one has taken up permanent residence.
If your supplies and equipment are cached securely, you will have a place, perhaps more than one, if you can afford several of these relatively inexpensive structures on cheaply obtained land, which you can go to if you must bug out from your primary residence.
An alternative, if it is too difficult to haul in concrete blocks and the things needed to make mortar and concrete, would be to use Earth Bag construction, in a similar manner.
There would need to be some modifications in design, if no concrete was used. Either the metal furnishings would have to be disassembled and cached, or enough Quik-Crete and welded fence wire brought in to make piers or slabs to which they can be attached, heavy enough to preclude the items from being lifted or turned over.
If the sand bags are left exposed, they could be burned, so either a fire resistant coating should be applied, stucco applied, or some other means to prevent fire on the inside from burning the sandbags and releasing the earth, which would collapse.
Alternatively, is enough Portland cement is brought in and a bit of water is available, stabilized earth can be mixed up and used to fill the bags, which, once placed and compacted slightly, will form into hard blocks and should stay in place even if the inside faces of the bags are burned.
Outside, berming or full earth cover would prevent much problem with the bags being burned, if stabilized earth is not used.
Just my opinion.