Two part closed cell spray foam is not like the one part "Great Stuff".
It won't absorb and hold moisture unless submerged for long periods of time. It also won't rust the steel like the single part "Great Stuff".
Here on skoolie.net we have researched and discussed this topic over and over again.
Closed cell, two part spray foam in a two pound density is the best there is for a skoolie conversion.
Best insulation for the floor is the blue 300 psi high density rigid Styrofoam sheets.
All that bubble wrap, tin foil faced styrofaom, tin foil with fiberglass inside, and insulation paints are all a farce. Nothing more than snake oil marketing scams.
Like East Coast CB said. Foil bubble wrap is good to block sunlight coming through a window, but is not real insulation.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization