Expanding foam sandwich between plastic wrap skin on frame

If you want to hide the fact you are sleeping in your vessel, you better not snore, or roll over in your sleep. As you get older, the former becomes more likely.

If society collapses, as you believe it will, any boat or structure, no matter how forgettable in appearance, might be something worth stealing or at least breaking into to see what is inside, such as food.

Assuming you are right about unrecoverable debt, many societies have dealt with debt that cannot be repaid in the obvious way: hyperinflation. People's monetary life savings become nearly worthless, but some sort of society remains.

Anyway, it seems to me that a real "survivalist", who thought the monetary system would collapse, would prepare by learning skills and caching and hiding supplies that can be bartered for other things. It's hard to do that living out of a tiny box, with no electric power, and no space or weight capacity for tools.

It might be difficult to find a life partner who wished to share your abode prior to the collapse. This is likely to be a solitary existence, and might remain so throughout your lifetime. Is it worth living?

There are so many possible end-of-the-world scenarios. A new disease that attacks people or their food sources or their shelters or their energy sources, a new religion or philosophy that encourages people to have many more children than the ecosystem can support, asteroid impact, runaway volcano-or-human induced greenhouse effect leading to something akin to the Permian extinction event, a new ice ball earth induced by asteroid impact or by people's attempts to reverse global warming (a la Snowpiercer), a huge tidal wave, evolution or creation of a harmful or more advanced species, foreign invasion, alien invasion or wiping out of life on earth, a massive coronal mass ejection that wipes out the electrical grid, a nearby supernova, discovery of a technology that wipes out your local economy, gang warfare, nuclear, chemical or biological war, the rise to power of a completely insane politician, a massive number of survivalists divorcing themselves from the local economy by living in tiny boxes , etc. All of these have a finite probability of occurring, therefore you might argue they eventually will. It is difficult to prepare for the right one(s), or to determine which will occur during your lifetime.