The next steps are all about real estate: location, location, location. You must strategically place yourself close enough that anyone wandering by might find you and give you some drugs. Plus, you can get a kick down for your space. Veins need to be warm so space inside your shopping cart villa may pay off if it is well constructed and safe from the elements. You must select a doorway or sidewalk that has limited foot traffic or the owners will surely call the cops. Finally, rest your cardboard on the tops of a hill. I have learned the hard way about people pissing above your stuff and how it rolls down hill.
Do not sleep next to garbage. Rats jump and like to tear up pieces of bedding for their nests. Do not sleep next to the curb. You will get soaked when street cleaning comes by in the morning.
In constructing the layers, cardboard goes down first. Then a wool type blanket. These blankets are extremely prone to body lice so try not to share them. The lice nestle in there until they find another host. A sleeping bag is optimal. You can also throw on two pairs of pants and four shirts. The effect is similar unless the sea breeze blows in at night. Then you need some type of tarp. A shopping cart is good for blocking the wind but not essential to the construction of your new digs.
Be sure to pack extra syringes, sterile water, a glass pipe, a push, cotton, some cookers, condoms, a candy bar, and some napkins. Like the Boy Scouts say- be prepared! Sleeping with a knife and a pitbull helps if you are going it alone.
I hope you never end up in these places. I've had a pink shopping cart, a battery generated shopping cart, a trunk on wheels. I can laugh at my insanity. The insanity that goes with active addiction.