Start with the conditions outside
Define the lowest temperatures, highest humidity, typical elevation, and how long the van may sit without shore power. Those conditions shape the heating load, water protection, ventilation, and energy reserve the build needs.
Treat comfort as a complete system
Insulation slows heat transfer, but heating, airflow, window coverage, and moisture management determine whether the cabin stays comfortable. Each choice affects the others and should be reviewed together.
Plan for recovery
Cold-weather equipment should remain serviceable when conditions are poor. Keep shutoffs, drains, filters, and critical controls accessible, and preserve a practical fallback when a primary system is unavailable.